Modified fluorinated nucleoside analogues

ABSTRACT

The disclosed invention provides compositions and methods of treating a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection in a host, including animals, and especially humans, using a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleosides, or a pharmaceutically acceptable salt or prodrug thereof.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit, pursuant to 35 U.S.C. §119(e), ofprovisional U.S. Patent Application Ser. No. 60/474,368, filed May 30,2003, the disclosure of which is hereby incorporated herein in itsentirety by reference.

FIELD OF THE INVENTION

The present invention includes (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleosides having the natural β-D configuration and methods for thetreatment of Flaviviridae infections, especially hepatitis C virus(HCV).

BACKGROUND OF THE INVENTION

Hepatitis C virus (HCV) infection is a major health problem that leadsto chronic liver disease, such as cirrhosis and hepatocellularcarcinoma, in a substantial number of infected individuals, estimated tobe 2-15% of the world's population. There are an estimated 4.5 millioninfected people in the United States alone, according to the U.S. Centerfor Disease Control. According to the World Health Organization, thereare more than 200 million infected individuals worldwide, with at least3 to 4 million people being infected each year. Once infected, about 20%of people clear the virus, but the rest can harbor HCV the rest of theirlives. Ten to twenty percent of chronically infected individualseventually develop liver-destroying cirrhosis or cancer. The viraldisease is transmitted parenterally by contaminated blood and bloodproducts, contaminated needles, or sexually and vertically from infectedmothers or carrier mothers to their offspring. Current treatments forHCV infection, which are restricted to immunotherapy with recombinantinterferon-α alone or in combination with the nucleoside analogribavirin, are of limited clinical benefit as resistance developsrapidly. Moreover, there is no established vaccine for HCV.Consequently, there is an urgent need for improved therapeutic agentsthat effectively combat chronic HCV infection.

The HCV virion is an enveloped positive-strand RNA virus with a singleoligoribonucleotide genomic sequence of about 9600 bases which encodes apolyprotein of about 3,010 amino acids. The protein products of the HCVgene consist of the structural proteins C, E1, and E2, and thenon-structural proteins NS2, NS3, NS4A and NS4B, and NS5A and NS5B. Thenonstructural (NS) proteins are believed to provide the catalyticmachinery for viral replication. The NS3 protease releases NS5B, theRNA-dependent RNA polymerase from the polyprotein chain. HCV NS5Bpolymerase is required for the synthesis of a double-stranded RNA from asingle-stranded viral RNA that serves as a template in the replicationcycle of HCV. Therefore, NS5B polymerase is considered to be anessential component in the HCV replication complex (K. Ishi, et al.,“Expression of Hepatitis C Virus NS5B Protein: Characterization of ItsRNA Polymerase Activity and RNA Binding,” Heptology, 29: 1227-1235(1999); V. Lohmann, et al., “Biochemical and Kinetic Analysis of NS5BRNA-Dependent RNA Polymerase of the Hepatitis C Virus,” Virology, 249:108-118 (1998)). Inhibition of HCV NS5B polymerase prevents formation ofthe double-stranded HCV RNA and therefore constitutes an attractiveapproach to the development of HCV-specific antiviral therapies.

HCV belongs to a much larger family of viruses that share many commonfeatures.

Flaviviridae Viruses

The Flaviviridae family of viruses comprises at least three distinctgenera: pestiviruses, which cause disease in cattle and pigs;flavivruses, which are the primary cause of diseases such as denguefever and yellow fever; and hepaciviruses, whose sole member is HCV. Theflavivirus genus includes more than 68 members separated into groups onthe basis of serological relatedness (Calisher et al., J. Gen. Virol,1993,70,37-43). Clinical symptoms vary and include fever, encephalitisand hemorrhagic fever (Fields Virology, Editors: Fields, B. N., Knipe,D. M., and Howley, P. M., Lippincott-Raven Publishers, Philadelphia,Pa., 1996, Chapter 31, 931-959). Flaviviruses of global concern that areassociated with human disease include the Dengue Hemorrhagic Feverviruses (DHF), yellow fever virus, shock syndrome and Japaneseencephalitis virus (Halstead, S. B., Rev. Infect. Dis., 1984, 6,251-264; Halstead, S. B., Science, 239:476-481, 1988; Monath, T. P., NewEng. J. Med, 1988, 319, 64 1-643).

The pestivirus genus includes bovine viral diarrhea virus (BVDV),classical swine fever virus (CSFV, also called hog cholera virus) andborder disease virus (BDV) of sheep (Moennig, V. et al. Adv. Vir. Res.1992, 41, 53-98). Pestivirus infections of domesticated livestock(cattle, pigs and sheep) cause significant economic losses worldwide.BVDV causes mucosal disease in cattle and is of significant economicimportance to the livestock industry (Meyers, G. and Thiel, H. J.,Advances in Virus Research, 1996, 47, 53-118; Moennig V., et al, Adv.Vir. Res. 1992, 41, 53-98). Human pestiviruses have not been asextensively characterized as the animal pestiviruses. However,serological surveys indicate considerable pestivirus exposure in humans.

Pestiviruses and hepaciviruses are closely related virus groups withinthe Flaviviridae family. Other closely related viruses in this familyinclude the GB virus A, GB virus A-like agents, GB virus-B and GBvirus-C (also called hepatitis G virus, HGV). The hepacivirus group(hepatitis C virus; HCV) consists of a number of closely related butgenotypically distinguishable viruses that infect humans. There are atleast 6 HCV genotypes and more than 50 subtypes. Due to the similaritiesbetween pestiviruses and hepaciviruses, combined with the poor abilityof hepaciviruses to grow efficiently in cell culture, bovine viraldiarrhea virus (BVDV) is often used as a surrogate to study the HCVvirus.

The genetic organization of pestiviruses and hepaciviruses is verysimilar. These positive stranded RNA viruses possess a single large openreading frame (ORF) encoding all the viral proteins necessary for virusreplication. These proteins are expressed as a polyprotein that is co-and post-translationally processed by both cellular and virus-encodedproteinases to yield the mature viral proteins. The viral proteinsresponsible for the replication of the viral genome RNA are locatedwithin approximately the carboxy-terminal. Two-thirds of the ORF aretermed nonstructural (NS) proteins. The genetic organization andpolyprotein processing of the nonstructural protein portion of the ORFfor pestiviruses and hepaciviruses is very similar. For both thepestiviruses and hepaciviruses, the mature nonstructural (NS) proteins,in sequential order from the amino-terminus of the nonstructural proteincoding region to the carboxy-terminus of the ORF, consist of p7, NS2,NS3, NS4A, NS4B, NS5A, and NS5B.

The NS proteins of pestiviruses and hepaciviruses share sequence domainsthat are characteristic of specific protein functions. For example, theNS3 proteins of viruses in both groups possess amino acid sequencemotifs characteristic of serine proteinases and of helicases (Gorbalenyaet al. (1988) Nature 333:22; Bazan and Fletterick (1989) Virology171:637-639; Gorbalenya et al. (1989) Nucleic Acid Res. 17.3889-3897).Similarly, the NS5B proteins of pestiviruses and hepaciviruses have themotifs characteristic of RNA-directed RNA polymerases (Koonin, E. V. andDolja, V. V. (1993) Crir. Rev. Biochem. Molec. Biol. 28:375-430).

The actual roles and functions of the NS proteins of pestiviruses andhepaciviruses in the lifecycle of the viruses are directly analogous. Inboth cases, the NS3 serine proteinase is responsible for all proteolyticprocessing of polyprotein precursors downstream of its position in theORF (Wiskerchen and Collett (1991) Virology 184:341-350; Bartenschlageret al. (1993) J. Virol. 67:3835-3844; Eckart et al. (1993) Biochem.Biophys. Res. Comm. 192:399-406; Grakoui et al. (1993) J. Virol.67:2832-2843; Grakoui et al. (1993) Proc. Natl. Acad. Sci. USA90:10583-10587; Hijikata et al. (1993) J. Virol. 67:4665-4675; Tome etal. (1993) J. Virol. 67:4017-4026). The NS4A protein, in both cases,acts as a cofactor with the NS3 serine protease (Bartenschlager et al.(1994) J. Virol. 68:5045-5055; Failla et al. (1994) J. Virol. 68:3753-3760; Xu et al. (1997) J. Virol. 71:53 12-5322). The NS3 protein ofboth viruses also functions as a helicase (Kim et al. (1995) Biochem.Biophys. Res. Comm. 215: 160-166; Jin and Peterson (1995) Arch. Biochem.Biophys., 323:47-53; Warrener and Collett (1995) J. Virol.69:1720-1726). Finally, the NS5B proteins of pestiviruses andhepaciviruses have the predicted RNA-directed RNA polymerases activity(Behrens et al. (1996) EMBO. 15:12-22; Lechmann et al. (1997) J. Virol.71:8416-8428; Yuan et al. (1997) Biochem. Biophys. Res. Comm.232:231-235; Hagedorn, PCT WO 97/12033; Zhong et al. (1998) J. Virol.72.9365-9369).

Treatment of HCV Infection with Interferon

Interferons (IFNs) have been commercially available for the treatment ofchronic hepatitis for nearly a decade. IFNs are glycoproteins producedby immune cells in response to viral infection. IFNs inhibit replicationof a number of viruses, including HCV, and when used as the soletreatment for hepatitis C infection, IFN can in certain cases suppressserum HCV-RNA to undetectable levels. Additionally, IFN can normalizeserum amino transferase levels. Unfortunately, the effect of IFN istemporary and a sustained response occurs in only 8%-9% of patientschronically infected with HCV (Gary L. Davis. Gastroenterology18:S104-S114, 2000). Most patients, however, have difficulty toleratinginterferon treatment, which causes severe flu-like symptoms, weightloss, and lack of energy and stamina.

A number of patents disclose Flaviviridae, including HCV, and treatmentsusing interferon-based therapies. For example, U.S. Pat. No. 5,980,884to Blatt et al. discloses methods for retreatment of patients afflictedwith HCV using consensus interferon. U.S. Pat. No. 5,942,223 to Bazer etal. discloses an anti-HCV therapy using ovine or bovine interferon-tau.U.S. Pat. No. 5,928,636 to Alber et al. discloses the combinationtherapy of interleukin-12 and interferon alpha for the treatment ofinfectious diseases including HCV. U.S. Pat. No. 5,849,696 to Chretienet al. discloses the use of thymosins, alone or in combination withinterferon, for treating HCV. U.S. Pat. No. 5,830,455 to Valtuena et al.discloses a combination HCV therapy employing interferon and a freeradical scavenger. U.S. Pat. No. 5,738,845 to Imakawa discloses the useof human interferon tau proteins for treating HCV. Otherinterferon-based treatments for HCV are disclosed in U.S. Pat. No.5,676,942 to Testa et al., U.S. Pat. No. 5,372,808 to Blatt et al., andU.S. Pat. No. 5,849,696. A number of patents also disclose pegylatedforms of interferon, such as U.S. Pat. Nos. 5,747,646, 5,792,834 and5,834,594 to Hoffmann-La Roche; PCT Publication No. WO 99/32139 and WO99/32140 to Enzon; WO 95/13090 and U.S. Pat. Nos. 5,738,846 and5,711,944 to Schering; and U.S. Pat. No. 5,908,621 to Glue et al.

Interferon alpha-2a and interferon alpha-2b are currently approved asmonotherapy for the treatment of HCV. ROFERON®-A (Roche) is therecombinant form of interferon alpha-2a. PEGASYS® (Roche) is thepegylated (i.e. polyethylene glycol modified) form of interferonalpha-2a. INTRON®A (Schering Corporation) is the recombinant form ofInterferon alpha-2b, and PEG-INTRON® (Schering Corporation) is thepegylated form of interferon alpha-2b.

Other forms of interferon alpha, as well as interferon beta, gamma, tauand omega are currently in clinical development for the treatment ofHCV. For example, INFERGEN (interferon alphacon-1) by InterMune,OMNIFERON (natural interferon) by Viragen, ALBUFERON by Human GenomeSciences, REBIF (interferon beta-1a) by Ares-Serono, Omega Interferon byBioMedicine, Oral Interferon Alpha by Amarillo Biosciences, andinterferon gamma, interferon tau, and interferon gamma-lb by InterMuneare in development.

Ribivarin

Ribavirin (1-β-D-ribofuranosyl-1-1,2,4-triazole-3-carboxamide) is asynthetic, non-interferon-inducing, broad spectrum antiviral nucleosideanalog sold under the trade name, Virazole (The Merck Index, 11thedition, Editor: Budavari, S., Merck & Co., Inc., Rahway, N.J., p 1304,1989). U.S. Pat. No. 3,798,209 and RE29,835 disclose and claimribavirin. Ribavirin is structurally similar to guanosine, and has invitro activity against several DNA and RNA viruses includingFlaviviridae (Gary L. Davis. Gastroenterology 118: 5104-51 14,2000).

Ribavirin reduces serum amino transferase levels to normal in 40% ofpatients, but it does not lower serum levels of HCV-RNA (Gary L. Davis,2000). Thus, ribavirin alone is not effective in reducing viral RNAlevels. Additionally, ribavirin has significant toxicity and is known toinduce anemia. Ribavirin is not approved for monotherapy against HCV. Ithas been approved in combination with interferon alpha-2a or interferonalpha-2b for the treatment of HCV.

Ribavirin is a known inosine monophosphate dehydrogenase inhibitor thatdoes not have specific anti-HCV activity in the HCV replicon system(Stuyver et al. Journal of Virology, 2003, 77, 10689-10694).

Combination of Interferon and Ribavirin

The current standard of care for chronic hepatitis C is combinationtherapy with an alpha interferon and ribavirin. The combination ofinterferon and ribavirin for the treatment of HCV infection has beenreported to be effective in the treatment of interferon naïve patients(Battaglia, A. M. et al., Ann. Pharmacother. 34:487-494, 2000), as wellas for treatment of patients when histological disease is present(Berenguer, M. et al. Antivir. Ther. 3(Suppl. 3):125-136, 1998). Studieshave shown that more patients with hepatitis C respond to pegylatedinterferon-alpha/ribavirin combination therapy than to combinationtherapy with unpegylated interferon alpha. However, as with monotherapy,significant side effects develop during combination therapy, includinghemolysis, flu-like symptoms, anemia, and fatigue. (Gary L. Davis,2000). Combination therapy with PEG-INTRON® (peginterferon alpha-2b) andREBETOL® (Ribavirin, USP) capsules are available from ScheringCorporation. REBETOL® (Schering Corporation) has also been approved incombination with INTRON® A (Interferon alpha-2b, recombinant, ScheringCorporation). Roche's PEGASYS® (pegylated interferon alpha-2a) andCOPEGUS® (ribavirin), as well as Three River Pharmacetical's Ribosphere®are also approved for the treatment of HCV.

PCT Publication Nos. WO 99/59621, WO 00/37110, WO 01/81359, WO 02/32414and WO 03/02446 1 by Schering Corporation disclose the use of pegylatedinterferon alpha and ribavirin combination therapy for the treatment ofHCV. PCT Publication Nos. WO 99/15 194, WO 99/64016, and WO 00/24355 byHoffmann-La Roche Inc. also disclose the use of pegylated interferonalpha and ribavirin combination therapy for the treatment of HCV.

Additional Methods to Treat Flaviviridae Infections

The development of new antiviral agents for Flaviviridae infections,especially hepatitis C, is currently underway. Specific inhibitors ofHCV-derived enzymes such as protease, helicase, and polymeraseinhibitors are being developed. Drugs that inhibit other steps in HCVreplication are also in development, for example, drugs that blockproduction of HCV antigens from the RNA (IRES inhibitors), drugs thatprevent the normal processing of HCV proteins (inhibitors ofglycosylation), drugs that block entry of HCV into cells (by blockingits receptor) and nonspecific cytoprotective agents that block cellinjury caused by the virus infection. Further, molecular approaches arealso being developed to treat hepatitis C, for example, ribozymes, whichare enzymes that break down specific viral RNA molecules, antisenseoligonucleotides, which are small complementary segments of DNA thatbind to viral RNA and inhibit viral replication, and RNA interferencetechniques are under investigation (Bymock et al. Antiviral Chemistry &Chemotherapy, 11:2; 79-95 (2000); De Francesco et al. in AntiviralResearch, 58: 1-16 (2003); and Kronke et al., J. Virol., 78:3436-3446(2004).

Bovine viral diarrhea virus (BVDV) is a pestivirus belonging to thefamily Flaviviridae and has been used as a surrogate for in vitrotesting of potential antiviral agents. While activity against BVDV maysuggest activity against other flaviviruses, often a compound can beinactive against BVDV and active against another flavivirus. Sommadossiand La Colla have revealed (“Methods and compositions for treatingflaviviruses and pestiviruses”, PCT WO 01/92282) that ribonucleosidescontaining a methyl group at the 2′ “up” position have activity againstBVDV. However, it is unclear whether these compounds can inhibit otherflaviviruses, including HCV in cell culture or at the HCV NS5B level.Interestingly while this publication discloses a large number ofcompounds that are 2′-methyl-2′-X-ribonucleosides, where X is a halogen,fluorine is not considered. Furthermore, a synthetic pathway leading tonucleosides halogenated at the 2′ “down” position is not shown by theseinventors.

Dengue virus (DENV) is the causative agent of Dengue hemorrhagic fever(DHF). According to the world Health Organization (WHO), two fifths ofthe world population are now at risk for infection with this virus. Anestimated 500,000 cases of DHF require hospitalization each year with amortality rate of 5% in children.

West Nile virus (WNV), a flavivirus previously known to exist only inintertropical regions, has emerged in recent years in temperate areas ofEurope and North America, presenting a threat to public health. The mostserious manifestation of WNV infection is fatal encephalitis in humans.Outbreaks in New York City and sporadic occurrences in the SouthernUnited States have been reported since 1999.

There is currently no preventive treatment of HCV, Dengue virus (DENV)or West Nile virus infection. Currently approved therapies, which existonly against HCV, are limited. Examples of antiviral agents that havebeen identified as active against the hepatitis C flavivirus include:

1) Protease inhibitors:

Substrate-based NS3 protease inhibitors (Attwood et al., PCT WO98/22496, 1998; Attwood et al., Antiviral Chemistry and Chemotherapy1999, 10, 259-273; Attwood et al., Preparation and use of amino acidderivatives as anti-viral agents, German Patent Pub. DE 19914474; Tunget al. Inhibitors of serine proteases, particularly hepatitis C virusNS3 protease, PCT WO 98/17679), including alphaketoamides andhydrazinoureas, and inhibitors that terminate in an electrophile such asa boronic acid or phosphonate (Llinas-Brunet et al., Hepatitis Cinhibitor peptide analogues, PCT WO 99/07734) are being investigated.

Non-substrate-based NS3 protease inhibitors such as2,4,6-trihydroxy-3-nitro-benzamide derivatives (Sudo K. et al.,Biochemical and Biophysical Research Communications, 1997, 238, 643-647;Sudo K. et al. Antiviral Chemistry and Chemotherapy, 1998, 9, 186),including RD3-4082 and RD3-4078, the former substituted on the amidewith a 14 carbon chain and the latter processing a para-phenoxyphenylgroup are also being investigated.

SCH 68631, a phenanthrenequinone, is an HCV protease inhibitor (Chu M.et al., Tetrahedron Letters 3 7:7229-7232, 1996). In another example bythe same authors, SCH 351633, isolated from the fungus Penicilliumgriseofulvum, was identified as a protease inhibitor (Chu M. et al.,Bioorganic and Medicinal Chemistry Letters 9:1949-1952). Nanomolarpotency against the HCV NS3 protease enzyme has been achieved by thedesign of selective inhibitors based on the macromolecule eglin c. Eglinc, isolated from leech, is a potent inhibitor of several serineproteases such as S. griseus proteases A and B, α-chymotrypsin, chymaseand subtilisin (Qasim M. A. et al., Biochemistry 36:1598-1607, 1997).

Several U.S. patents disclose protease inhibitors for the treatment ofHCV. For example, U.S. Pat. No. 6,004,933 to Spruce et al. discloses aclass of cysteine protease inhibitors for inhibiting HCV endopeptidase2. U.S. Pat. No. 5,990,276 to Zhang et al. discloses syntheticinhibitors of hepatitis C virus NS3 protease. The inhibitor is asubsequence of a substrate of the NS3 protease or a substrate of theNS4A cofactor. The use of restriction enzymes to treat HCV is disclosedin U.S. Pat. No. 5,538,865 to Reyes et al. Peptides as NS3 serineprotease inhibitors of HCV are disclosed in WO 02/008251 to CorvasInternational, Inc. and WO 02/08187 and WO 02/008256 to ScheringCorporation. HCV inhibitor tripeptides are disclosed in U.S. Pat. Nos.6,534,523, 6,410,531, and 6,420,380 to Boehringer Ingelheim and WO02/060926 to Bristol Myers Squibb. Diaryl peptides as NS3 serineprotease inhibitors of HCV are disclosed in WO 02/48172 to ScheringCorporation. Imidazoleidinones as NS3 serine protease inhibitors of HCVare disclosed in WO 02/08198 to Schering Corporation and WO 02/48157 toBristol Myers Squibb. WO 98/17679 to Vertex Pharmaceuticals and WO02/48116 to Bristol Myers Squibb also disclose HCV protease inhibitors.

2) Thiazolidine derivatives which show relevant inhibition in areverse-phase HPLC assay with an NS3/4A fusion protein and NS5A/5Bsubstrate (Sudo K. et al., Antiviral Research, 1996, 32, 9-18),especially compound RD-1-6250, possessing a fused cinnamoyl moietysubstituted with a long alkyl chain, RD4 6205 and RD4 6193;3) Thiazolidines and benzanilides identified in Kakiuchi N. et al. J.EBS Letters 421, 217-220; Takeshita N. et al. Analytical Biochemistry,1997, 247,242-246;4) A phenanthrenequinone possessing activity against protease in aSDS-PAGE and autoradiography assay isolated from the fermentationculture broth of Streptomyces sp., Sch 68631 (Chu M. et al., TetrahedronLetters, 1996, 37, 7229-7232), and Sch 351633, isolated from the fungusPenicillium griseofulvum, which demonstrates activity in a scintillationproximity assay (Chu M. et al., Bioorganic and Medicinal ChemistryLetters 9, 1949-1952);5) Helicase inhibitors (Diana G. D. et al., Compounds, compositions andmethods for treatment of hepatitis C, U.S. Pat. No. 5,633,358; Diana G.D. et al., Piperidine derivatives, pharmaceutical compositions thereofand their use in the treatment of hepatitis C, PCT WO 97/36554);6) Nucleotide polymerase inhibitors and gliotoxin (Ferrari R. et al.Journal of Virology, 1999, 73, 1649-1654), and the natural productcerulenin (Lohmann V. et al, Virology, 1998, 249, 108-118);7) Antisense phosphorothioate oligodeoxynucleotides (S-ODN)complementary to sequence stretches in the 5′ non-coding region (NCR) ofthe virus (Alt M. et al., Hepatology, 1995, 22, 707-717), or nucleotides326-348 comprising the 3′ end of the NCR and nucleotides 371-388 locatedin the core coding region of the HCV RNA (Alt M. et al., Archives ofVirology, 1997, 142, 589-599; Galderisi U. et al., Journal of CellularPhysiology, 1999, 181, 251-257);8) Inhibitors of IRES-dependent translation (Ikeda N. et al., Agent forthe prevention and treatment of hepatitis C, Japanese Patent Pub.JP-8268890; Kai Y. et al. Prevention and treatment of viral diseases,Japanese Patent Pub. JP-101 01591);9) Ribozymes, such as nuclease-resistant ribozymes (Maccjak, D. J. etal., Hepatology 1999, 30, abstract 995) and those disclosed in U.S. Pat.No. 6,043,077 to Barber et al., and U.S. Pat. Nos. 5,869,253 and5,610,054 to Draper et al.;10) Nucleoside analogs have also been developed for the treatment ofFlaviviridae infections.

Idenix Pharmaceuticals discloses the use of certain branched nucleosidesin the treatment of flaviviruses (including HCV) and pestiviruses inInternational Publication Nos. WO 01/90121 and WO 01/92282.Specifically, a method for the treatment of hepatitis C virus infection(and flaviviruses and pestiviruses) in humans and other host animals isdisclosed in the Idenix publications that includes administering aneffective amount of a biologically active 1′, 2′, 3′ or 4′-branched β-Dor β-L nucleosides or a pharmaceutically acceptable salt or derivativethereof, administered either alone or in combination with anotherantiviral agent, optionally in a pharmaceutically acceptable carrier.

WO 2004/002422 to Idenix published Jan. 8, 2004 discloses a family of2′-methyl nucleosides for the treatment of flavivirus infections. WO2004/002999 to Idenix, published Jan. 8, 2004 discloses a series of 2′or 3′ prodrugs of 1′, 2′, 3′, or 4′ branch nucleosides for the treatmentof flavivirus infections including HCV infections.

Other patent applications disclosing the use of certain nucleosideanalogs to treat hepatitis C virus infection include: PCT/CAOO/01316 (WO01/32153; filed Nov. 3, 2000) and PCT/CAOI/00197 (WO 01/60315; filedFeb. 19, 2001) filed by BioChem Pharma, Inc. (now Shire Biochem, Inc.);PCT/US02/01531 (WO 02/057425; filed Jan. 18, 2002) and PCT/U502/03086(WO 02/057287; filed Jan. 18, 2002) filed by Merck & Co., Inc.,PCT/EPOT/09633 (WO 02/18404; published Aug. 21, 2001) filed by Roche,and PCT Publication Nos. WO 01/79246 (filed Apr. 13, 2001), WO 02/32920(filed Oct. 18, 2001) and WO 02/48 165 by Pharmasset, Ltd.

WO 2004/007512 to Merck & Co. discloses a number of nucleoside compoundsdisclosed as inhibitors of RNA-dependent RNA viral polymerase. Thenucleosides disclosed in this publication are primarily2′-methyl-2′-hydroxy substituted nucleosides. WO 02/057287 to Merck etal. published Jul. 25, 2002, discloses a large genus of pyrimidinederivative nucleosides of the 2′-methyl-2′-hydroxy substitutions. WO2004/009020 to Merck et al. discloses a series of thionucleosidederivatives as inhibitors of RNA dependent RNA viral polymerase. WO03/105770 to Merck et al. discloses a series of carbocyclic nucleosidederivatives that are useful for the treatment of HCV infections.

PCT Publication No. WO 99/43691 to Emory University, entitled“2′-Fluoronucleosides” discloses the use of certain 2′-fluoronucleosidesto treat HCV. U.S. Pat. No. 6,348,587 to Emory University entitled“2′-fluoronucleosides” discloses a family of 2′-fluoronucleosides usefulfor the treatment of hepatitis B, HCV, HIV and abnormal cellularproliferation. The 2′ substitutent is disclosed to be in either the “up”or “down” position.

Eldrup et al. (Oral Session V, Hepatitis C Virus, Flaviviridae; 16^(th)International Conference on Antiviral Research (Apr. 27, 2003, Savannah,Ga.)) described the structure activity relationship of 2′-modifiednucleosides for inhibition of HCV.

Bhat et al. (Oral Session V, Hepatitis C Virus, Flaviviridae; 16^(th)International Conference on Antiviral Research (Apr. 27, 2003, Savannah,Ga.); p A75) describe the synthesis and pharmacokinetic properties ofnucleoside analogues as possible inhibitors of HCV RNA replication. Theauthors report that 2′-modified nucleosides demonstrate potentinhibitory activity in cell-based replicon assays.

Olsen et al. (Oral Session V, Hepatitis C Virus, Flaviviridae; 16^(th)International Conference on Antiviral Research (Apr. 27, 2003, Savannah,Ga.) p A76) also described the effects of the 2′-modified nucleosides onHCV RNA replication.

11) Other miscellaneous compounds including 1-amino-alkylcyclohexanes(U.S. Pat. No. 6,034,134 to Gold et al.), alkyl lipids (U.S. Pat. No.5,922,757 to Chojkier et al.), vitamin E and other antioxidants (U.S.Pat. No. 5,922,757 to Chojkier et al.), squalene, amantadine, bile acids(U.S. Pat. No. 5,846,964 to Ozeki et al.),N-(phosphonoacetyl)-L-aspartic acid, (U.S. Pat. No. 5,830,905 to Dianaet al.), benzenedicarboxamides (U.S. Pat. No. 5,633,388 to Diana etal.), polyadenylic acid derivatives (U.S. Pat. No. 5,496,546 to Wang etal.), 2,3-dideoxyinosine (U.S. Pat. No. 5,026,687 to Yarchoan et al.),benzimidazoles (U.S. Pat. No. 5,891,874 to Colacino et al.), plantextracts (U.S. Pat. No. 5,837,257 to Tsai et al., U.S. Pat. No.5,725,859 to Omer et al., and U.S. Pat. No. 6,056,961), and piperidenes(U.S. Pat. No. 5,830,905 to Diana et al.).12) Other compounds currently in preclinical or clinical development fortreatment of hepatitis C virus infection include: Interleukin-10 bySchering-Plough, IP-SOI by Intemeuron, Merimebodib (VX-497) by Vertex,AMANTADINE® (Symmetrel) by Endo Labs Solvay, HEPTAZYME® by RPI, IDN-6556by Idun Pharma., XTL-002 by XTL., HCV/MFS9 by Chiron, CIVACIR®(hepatitis C Immune Globulin) by NABI, LEVOVIRIN® by ICN/Ribaphamm,VIRAMIDINE® by ICN/Ribapharm, ZADAXIN® (thymosin alpha-1) by SciClone,thymosin plus pegylated interferon by Sci Clone, CEPLENE® (histaminedihydrochloride) by Maxim, VX 950/LY 570310 by Vertex/Eli Lilly, ISIS14803 by Isis Pharmaceutical/Elan, IDN-6556 by Idun Pharmaceuticals,Inc., JTK 003 by AKROS Pharma, BILN-2061 by Boehringer Ingelheim,CellCept (mycophenolate mofetil) by Roche, T67, a β-tubulin inhibitor,by Tularik, a therapeutic vaccine directed to E2 by Innogenetics, FK788by Fujisawa Healthcare, Inc., 1 dB 1016 (Siliphos, oralsilybin-phosphatdylcholine phytosome), RNA replication inhibitors(VP50406) by ViroPharma/Wyeth, therapeutic vaccine by Intercell,therapeutic vaccine by Epimmune/Genencor, IRES inhibitor by Anadys, ANA245 and ANA 246 by Anadys, immunotherapy (Therapore) by Avant, proteaseinhibitor by Corvas/SChering, helicase inhibitor by Vertex, fusioninhibitor by Trimeris, T cell therapy by CellExSys, polymerase inhibitorby Biocryst, targeted RNA chemistry by PTC Therapeutics, Dication byImmtech, Int., protease inhibitor by Agouron, protease inhibitor byChiron/Medivir, antisense therapy by AVI BioPharma, antisense therapy byHybridon, hemopurifier by Aethlon Medical, therapeutic vaccine by Merix,protease inhibitor by Bristol-Myers Squibb/Axys, Chron-VacC, atherapeutic vaccine, by Tripep, UT 231 B by United Therapeutics,protease, helicase and polymerase inhibitors by Genelabs Technologies,IRES inhibitors by Immusol, R803 by Rigel Pharmaceuticals, INFERGEN®(interferon alphacon-1) by InterMune, OMNIERON® (natural interferon) byViragen, ALBUFERON® by Human Genome Sciences, REBIF® (interferonbeta-1a) by Ares-Serono, Omega Interferon by BioMedicine, OralInterferon Alpha by Amarillo Biosciences, interferon gamma, interferontau, and Interferon gamma-1b by InterMune. Rigel Pharmaceuticals isdeveloping a non-nucleoside HCV polymerase inhibitor, R803, that showspromise as being synergistic with IFN and ribavirin.13) A summary of several investigational drugs, including severaldiscussed above, that are currently in various phases of development forthe treatment of HCV, are summarized below:

Drug Mechanism/Target Company U.S. Status BILN-2061 NS3 Serine-proteaseBoehringer Phase II inhibitor Ingelheim ISIS 14803 Antisense/PreventISIS/Elan Phase II Translation of RNA Viramidine Prodrug of RibavirinRibapharm Phase II NM 283 Inhibitor of HCV RNA Idenix Phase II/IIIPolymerase VX-497 IMPDH Inhibitor Vertex Phase I/II JKT-003 Inhibitor ofHCV RNA Japan Tobacco/ Phase I/II Polymerase Akros Levovirin L-Ribavirinanalog Ribapharm/Roche Phase I/II Isatoribine; Nucleoside analog AnadysPhase I ANA245 Interact with TLR7 receptor Albuferon Immune modulatorHuman Genome Phase I Sciences Peg-Infergen Immune modulator IntermunePhase I VX-950 Inhibitor of HCV Vertex Preclinical NS3-4A protease SCH 6Inhibitor of HCV Schering Plough Preclinical NS3-4A protease R803Inhibitor of HCV RNA Rigel Phase I polymerase HCV-086 — ViroPharma/WyethPhase I R1479 Inhibitor of HCV RNA Roche Phase I polymerase

Nucleoside prodrugs have been previously described for the treatment ofother forms of hepatitis. WO 00/09531 and WO 01/96353 to IdenixPharmaceuticals, discloses 2′-deoxy-β-L-nucleosides and their3′-prodrugs for the treatment of HBV. U.S. Pat. No. 4,957,924 toBeauchamp discloses various therapeutic esters of acyclovir.

In light of the fact that HCV infection has reached epidemic levelsworldwide, and has tragic effects on the infected patient, there remainsa strong need to provide new effective pharmaceutical agents to treathepatitis C that have low toxicity to the host.

Further, given the rising threat of other flaviviridae infections, thereremains a strong need to provide new effective pharmaceutical agentsthat have low toxicity to the host.

SUMMARY OF THE INVENTION

There is currently no preventive treatment of Hepatitis C virus (HCV),Dengue virus (DENV) or West Nile virus (WNV) infection, and currentlyapproved therapies, which exist only against HCV, are limited. Designand development of pharmaceutical compounds is essential, especiallythose that are synergistic with other approved and investigationalFlaviviridae, and in particular HCV, therapeutics for the evolution oftreatment standards, including more effective combination therapies.

The present invention provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside (β-D or β-L), or its pharmaceutically acceptable salt orprodrug thereof, and the use of such compounds for the treatment of ahost infected with a virus belonging to the Flaviviridae family,including hepatitis C, West Nile Virus and yellow fever virus. Inaddition, the nucleosides of the present invention show actively againstrhinovirus. Rhinoviruses (RVs) are small (30 nm), nonenveloped virusesthat contain a single-strand ribonucleic acid (RNA) genome within anicosahedral (20-sided) capsid. RVs belong to the Picornaviridae family,which includes the genera Enterovirus (polioviruses, coxsackievirusesgroups A and B, echoviruses, numbered enteroviruses) and Hepatovirus(hepatitis A virus). Approximately 101 serotypes are identifiedcurrently. Rhinoviruses are most frequently associated with the commoncold, nasopharyngitis, croup, pneumonia, otitis media and asthmaexacerbations.

The inventor has made the unexpected discovery that the 2′ substitutionson the β-D or β-L nucleosides of the present invention impart greaterspecificity for hepatitis C virus as well as exhibiting lower toxicityfollowing administration to a host. The invention also includes a methodfor treating a Flaviviridae infection, including hepatitis C virus, WestNile Virus and yellow fever virus and rhinovirus infection, thatincludes the administration of an anti-virally effective amount of a β-Dor β-L nucleoside disclosed herein, or its pharmaceutically acceptablesalt or prodrug, optionally in a pharmaceutically acceptable carrier ordiluent, optionally in combination or alternation with another effectiveantiviral agent.

The nucleosides of the present invention, possess the unique propertiesof having greater specificity for the hepatitis C virus and lowertoxicity in culture or when administered into an animal. One potential,but non-limiting reason for this is the presence of the 2′-fluorosubstitution on the ribose ring. For example, U.S. Pat. No. 6,348,587 toSchinazi et al., discloses a family of 2′-fluoro nucleoside compoundsthat are useful in the treatment of hepatitis C virus infection. Incontrast, are 2′-methyl substitutions such as found in2′-C-methylcytidine as shown in WO 2004/02999 to Idenix wherein the2′-methyl substitution on the nucleoside ring at the 2′ position is notspecific to hepatitis C.

Thus, in one aspect, the antivirally effective nucleoside is a(2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L) or itspharmaceutically acceptable salt or prodrug thereof of the generalformula:

-   -   wherein    -   (a) Base is a naturally occurring or modified purine or        pyrimidine base;    -   (b) X is O, S, CH₂, Se, NH, N-alkyl, CHW (R, S, or racemic),        C(W)₂, wherein W is F, Cl, Br, or I;    -   (c) R¹ and R⁷ are independently H, phosphate, including        5′-monophosphate, diphosphate, triphosphate, or a stabilized        phosphate prodrug, H-phosphonate, including stabilized        H-phosphonates, acyl, including optionally substituted phenyl        and lower acyl, alkyl, including lower alkyl, O-substituted        carboxyalkylamino or its peptide derivatives, sulfonate ester,        including alkyl or arylalkyl sulfonyl, including methanesulfonyl        and benzyl, wherein the phenyl group is optionally substituted,        a lipid, including a phospholipid, an L or D-amino acid, a        carbohydrate, a peptide, a cholesterol, or other        pharmaceutically acceptable leaving group which when        administered in vivo is capable of providing a compound wherein        R¹ is H or phosphate; R² is OH or phosphate; R¹ and R² or R⁷ can        also be linked with cyclic phosphate group; and    -   (d) R² and R^(2′) are independently H, C₁₋₄ alkyl, C₁₋₄ alkenyl,        C₁₋₄ alkynyl, vinyl, N₃, CN, Cl, Br, F, I, NO₂, C(O)O(C₁₋₄        alkyl), C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄ alkynyl), C(O)O(C₁₋₄        alkenyl), O(C₁₋₄ acyl), O(C₁₋₄ alkyl), O(C₁₋₄ alkenyl), S(C₁₋₄        acyl), S(C₁₋₄ alkyl), S(C₁₋₄ alkynyl), S(C₁₋₄ alkenyl), SO(C₁₋₄        acyl), SO(C₁₋₄ alkyl), SO(C₁₋₄ alkynyl), SO(C₁₋₄ alkenyl),        SO₂(C₁₋₄ acyl), SO₂(C₁₋₄ alkyl), SO₂(C₁₋₄ alkynyl), SO₂(C₁₋₄        alkenyl), O₃S(C₁₋₄ acyl), O₃S(C₁₋₄ alkyl), O₃S(C₁₋₄ alkenyl),        NH₂, NH(C₁₋₄ alkyl), NH(C₁₋₄ alkenyl), NH(C₁₋₄ alkynyl), NH(C₁₋₄        acyl), N(C₁₋₄ alkyl)₂, N(C₁₋₁₈ acyl)₂, wherein alkyl, alkynyl,        alkenyl and vinyl are optionally substituted by N₃, CN, one to        three halogen (Cl, Br, F, I), NO₂, C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄        alkyl), C(O)O(C₁₋₄ alkynyl), C(O)O(C₁₋₄ alkenyl), O(C₁₋₄ acyl),        O(C₁₋₄ alkyl), O(C₁₋₄ alkenyl), S(C₁₋₄ acyl), S(C₁₋₄ alkyl),        S(C₁₋₄ alkynyl), S(C₁₋₄ alkenyl), SO(C₁₋₄ acyl), SO(C₁₋₄ alkyl),        SO(C₁₋₄ alkynyl), SO(C₁₋₄ alkenyl), SO₂(C₁₋₄ acyl), SO₂(C₁₋₄        alkyl), SO₂(C₁₋₄ alkynyl), SO₂(C₁₋₄ alkenyl), O₃S(C₁₋₄ acyl),        O₃S(C₁₋₄ alkyl), O₃S(C₁₋₄ alkenyl), NH₂, NH(C₁₋₄ alkyl), NH(C₁₋₄        alkenyl), NH(C₁₋₄ alkynyl), NH(C₁₋₄ acyl), N(C₁₋₄ alkyl)₂,        N(C₁₋₄ acyl)₂, R² and R^(2′) can be together to form a vinyl        optionally substituted by one or two of N₃, CN, Cl, Br, F, I,        NO₂; OR⁷ and    -   (e) R⁶ is an optionally substituted alkyl (including lower        alkyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH),        fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃,        CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro.

In various aspects of the invention, the Base can be selected from

wherein

-   -   (a) Y is N or CH.    -   (b) R³, R⁴ and R⁵ are independently H, halogen (including F, Cl,        Br, I), OH, OR′, SH, SR′, NH₂, NHR′, NR′₂, lower alkyl of C₁-C₆,        halogenated (F, Cl, Br, I) lower alkyl of C₁-C₆ such as CF₃ and        CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH═CH₂, halogenated (F,        Cl, Br, I) lower alkenyl of C₂-C₆ such as CH═CHCl, CH═CHBr and        CH═CHI, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, Cl,        Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C₁-C₆ such as        CH₂OH and CH₂CH₂OH, halogenated (F, Cl, Br, I) lower alkoxy of        C₁-C₆, CO₂H, CO₂R′, CONH₂, CONHR′, CONR′₂, CH═CHCO₂H,        CH═CHCO₂R′;    -   wherein R′ is an optionally substituted alkyl of C₁-C₁₂        (particularly when the alkyl is an amino acid residue),        cycloalkyl, optionally substituted alkynyl of C₂-C₆, optionally        substituted lower alkenyl of C₂-C₆, or optionally substituted        acyl.

In still another aspect, the (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereofcan be of the formula:

-   -   wherein    -   (a) Base, Y, R¹, R², R^(2′), R³, R⁴, R⁵, R⁶, R⁷ and R′ are as        described above.

Various aspects of the present invention also include pharmaceuticalcompositions comprising any of the (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside (β-D or β-L) described herein or their pharmaceuticallyacceptable salts or prodrugs thereof and a pharmaceutically acceptablecarrier.

The present invention also provides in various aspects, methods for thetreatment or prophylaxis of hepatitis C virus infection, West Nile virusinfection, a yellow fever viral infection or a rhinovirus infectioncomprising administering to a host an antivirally effective amount of a(2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside disclosed herein. Theinvention also includes methods for treating or preventing Flaviviridaeinfection, including all members of the Hepacivirus genus (HCV),Pestivirus genus (BVDV, CSFV, BDV), or Flavivirus genus (Dengue virus,Japanese encephalitis virus group (including West Nile Virus), andYellow Fever virus).

In various aspects, the (2′R)-2′-deoxy-2′-fluoro-2′-C-methylβ-D-nucleoside has an EC₅₀ (effective concentration to achieve 50%inhibition) when tested in an appropriate cell-based assay, of less than15 micromolar, and more particularly, less than 10 or 5 micromolar. Inother aspects, the nucleoside is enantiomerically enriched.

The present invention also provides methods for the treatment orprophylaxis of a hepatitis C virus infection, West Nile virus infection,a yellow fever viral infection or a rhinovirus infection in a hostcomprising administering an effective amount of a(2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleosides (β-D or β-L) disclosedherein, or its pharmaceutically acceptable salt or prodrug thereof, incombination or alternation with one or more other effective antiviralagent(s), optionally in a pharmaceutically acceptable carrier or diluentthereof, as described herein. Nonlimiting examples of the types ofantiviral agents or their prodrugs that can be used in combination withthe compounds disclosed herein include, but are not limited to:interferon, including interferon alpha 2a, interferon alpha 2b, apegylated interferon, interferon beta, interferon gamma, interferon tauand interferon omega; an interleukin, including interleukin 10 andinterleukin 12; ribavirin; interferon in combination with ribavirin; aprotease inhibitor including NS3 inhibitor; a helicase inhibitor; apolymerase inhibitor; gliotoxin; an IRES inhibitor; and antisenseoligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme;another nucleoside, nucleoside prodrug or nucleoside derivative; a1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene;amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; abenzenedicarboxamide; polyadneylic acid; a benzimidazoles; thymosin; abeta tubulin inhibitor; a prophylactic vaccine;silybin-phosphatidlycholine phytosome; and mycophenolate.

The following non-limiting aspects illustrate some general methodologyto obtain the nucleosides of the present invention. Specifically, thesynthesis of the present nucleosides can be achieved by either of twogeneral means:

1) alkylating the appropriately modified carbohydrate building block,subsequent fluorination, followed by coupling to form the nucleosides ofthe present invention (Scheme 1) or

2) glycosylation to form the nucleoside followed by alkylation andfluorination of the pre-formed nucleosides of the present invention(Scheme 2).

In addition, the L-enantiomers corresponding to the compounds of theinvention can be prepared following the same general methods (Schemes 1or 2), beginning with the corresponding L-carbohydrate building block ornucleoside L-enantiomer as the starting material.

Thus, the present invention includes at least the following generalfeatures:

-   -   (a) β-D and β-L nucleosides of the general formulas disclosed,        or their pharmaceutically acceptable salts or prodrugs thereof,        as described herein;    -   (b) processes for the preparation of the β-D and β-L nucleosides        of the general formula disclosed, or their pharmaceutically        acceptable salts or prodrugs thereof, as described herein;    -   (c) pharmaceutical compositions comprising a β-D or β-L        nucleoside of the general formulas disclosed, or its        pharmaceutically acceptable salt or prodrug thereof, in a        pharmaceutically acceptable carrier or diluent thereof, as        described herein, for the treatment or prophylaxis of a viral        infection in a host;    -   (d) pharmaceutical compositions comprising a β-D or β-L        nucleoside of the general formulas disclosed, or its        pharmaceutically acceptable salt or prodrug thereof, in        combination with one or more other effective antiviral agent(s),        optionally in a pharmaceutically acceptable carrier or diluent        thereof, as described herein, for the treatment or prophylaxis        of a viral infection in a host;    -   (e) methods for the treatment or prophylaxis of a Flaviviridae        infection, including hepatitis C virus, West Nile Virus and        yellow fever virus and rhinovirus infection in a host comprising        administering an effective amount of a β-D or β-L nucleoside of        the general formulas disclosed, or its pharmaceutically        acceptable salt or prodrug thereof, optionally in a        pharmaceutically acceptable carrier or diluent thereof, as        described herein;    -   (f) methods for the treatment or prophylaxis of a Flaviviridae        infection, including hepatitis C virus, West Nile Virus and        yellow fever virus and rhinovirus infection in a host comprising        administering an effective amount of a β-D or β-L nucleoside of        the general formulas disclosed, or its pharmaceutically        acceptable salt or prodrug thereof, in combination or        alternation with one or more other effective antiviral agent(s),        optionally in a pharmaceutically acceptable carrier or diluent        thereof, as described herein;    -   (g) use of a β-D or β-L nucleoside of the general formulas        disclosed, or its pharmaceutically acceptable salt or prodrug        thereof, optionally in a pharmaceutically acceptable carrier, as        described herein, for the treatment or prophylaxis of a        Flaviviridae infection, including hepatitis C virus, West Nile        Virus and yellow fever virus and rhinovirus infection in a host;    -   (h) use of a β-D or β-L nucleoside of the general formulas        disclosed, or its pharmaceutically acceptable salt or prodrug        thereof, in combination or alternation with one or more other        effective antiviral agent(s), optionally in a pharmaceutically        acceptable carrier, as described herein, for the treatment or        prophylaxis of a Flaviviridae infection, including hepatitis C        virus, West Nile Virus and yellow fever virus and rhinovirus        infection in a host;    -   (i) use of a β-D or β-L nucleoside of the general formulas        disclosed, or its pharmaceutically acceptable salt or prodrug        thereof, optionally in a pharmaceutically acceptable carrier, as        described herein, in the manufacture of a medicament for the        treatment or prophylaxis of a Flaviviridae infection, including        hepatitis C virus, West Nile Virus and yellow fever virus and        rhinovirus infection in a host;    -   (j) use of a β-D or β-L nucleoside of the general formulas        disclosed, or its pharmaceutically acceptable salt or prodrug        thereof, in combination or alternation with one or more other        effective antiviral agent(s), optionally in a pharmaceutically        acceptable carrier, as described herein, in the manufacture of a        medicament for the treatment or prophylaxis of a Flaviviridae        infection, including hepatitis C virus, West Nile Virus and        yellow fever virus and rhinovirus infection in a host;    -   (k) use of a β-D or β-L nucleoside of the general formulas        disclosed, or its pharmaceutically acceptable salt or prodrug        thereof, optionally in a pharmaceutically acceptable carrier or        diluent, as described herein, in a medical therapy, i.e. as        antiviral for example for the treatment or prophylaxis of a        Flaviviridae infection, including hepatitis C virus, West Nile        Virus and yellow fever virus and rhinovirus infection;    -   (l) use of a β-D or β-L nucleoside of the general formulas        disclosed, as described herein, or its pharmaceutically        acceptable salt or prodrug thereof, i.e. as antiviral agent, in        combination or alternation with one or more other effective        therapeutic agent(s), i.e. another antiviral agent, optionally        in a pharmaceutically acceptable carrier or diluent, as        described herein, in a medical therapy, for example for the        treatment or prophylaxis of a Flaviviridae infection, including        hepatitis C virus, West Nile Virus and yellow fever virus and        rhinovirus infection in a host.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graphical depiction of the dose-dependant reduction of thereplicon HCV RNA based on the treatment withβ-D-(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine. (A): The viralreduction was compared to the reduction of cellular RNA levels(ribosomal RNA) to obtain therapeutic index values. EC₉₀ whichrepresents the effective concentration 90% at 96 hours following thedose dependant administration of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine was determined to be 5 μM.(B): HCV RNA was significantly reduced in a dose-dependent manner for 7days following treatment with 25 μM.

FIG. 2 depicts the average weight change (%) of female Swiss mice in thetoxicity study of β-D-(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine atvarious doses. Intraperitneal injections were given on days 0 to day 5of the 0, 3.3, 10, 33, 100 mg/kg. Each dosing group contained 5 mice andno mice died during the 30-day study.

FIG. 3 depicts the pharmacokinetics ofβ-D-(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine in Rhesus monkeys givena single dose (33.3 mg/kg) oral or intravenous dose ofβ-D-(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the invention are now described in detail. Asused in the description herein and throughout the claims that follow,the meaning of “a,” “an,” and “the” includes plural reference unless thecontext clearly dictates otherwise. Also, as used in the descriptionherein and throughout the claims that follow, the meaning of “in”includes “in” and “on” unless the context clearly dictates otherwise.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the invention, and in thespecific context where each term is used. Certain terms that are used todescribe the invention are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitioner indescribing the compositions and methods of the invention and how to makeand use them. For convenience, certain terms may be highlighted, forexample using italics and/or quotation marks. The use of highlightinghas no influence on the scope and meaning of a term; the scope andmeaning of a term is the same, in the same context, whether or not it ishighlighted. It will be appreciated that the same thing can be said inmore than one way. Consequently, alternative language and synonyms maybe used for any one or more of the terms discussed herein, nor is anyspecial significance to be placed upon whether or not a term iselaborated or discussed herein. Synonyms for certain terms are provided.A recital of one or more synonyms does not exclude the use of othersynonyms. The use of examples anywhere in this specification, includingexamples of any terms discussed herein, is illustrative only, and in noway limits the scope and meaning of the invention or of any exemplifiedterm. Likewise, the invention is not limited to various embodimentsgiven in this specification.

As used herein, “about” or “approximately” shall generally mean within20 percent, preferably within 10 percent, and more preferably within 5percent of a given value or range. Numerical quantities given herein areapproximate, meaning that the term “about” or “approximately” can beinferred if not expressly stated.

The present invention provides (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleosides and their pharmaceutically acceptable salts and prodrugs forthe treatment of hepatitis C virus infection, West Nile virus infection,a yellow fever viral infection or a rhinovirus infection in a host.

The disclosed compounds or their pharmaceutically acceptable derivativesor salts or pharmaceutically acceptable formulations containing thesecompounds are useful in the prevention and treatment of HCV infections.In addition, these compounds or formulations can be usedprophylactically to prevent or retard the progression of clinicalillness in individuals who are anti-HCV antigen positive or who havebeen exposed to HCV.

The compounds disclosed herein can be converted into a pharmaceuticallyacceptable ester by reaction with an appropriate esterifying agent, forexample, an acid halide or anhydride. The compound or itspharmaceutically acceptable derivative can be converted into apharmaceutically acceptable salt thereof in a conventional manner, forexample, by treatment with an appropriate base. The ester or salt of thecompound can be converted into the parent compound, for example, byhydrolysis.

DEFINITIONS

The term “independently” is used herein to indicate that the variable,which is independently applied, varies independently from application toapplication. Thus, in a compound such as R^(a)XYR^(a), wherein R^(a) is“independently carbon or nitrogen”, both R^(a) can be carbon, both R^(a)can be nitrogen, or one R^(a) can be carbon and the other R^(a)nitrogen.

As used herein, the terms “enantiomerically pure” or “enantiomericallyenriched” refers to a nucleoside composition that comprises at leastapproximately 95%, and preferably approximately 97%, 98%, 99% or 100% ofa single enantiomer of that nucleoside.

As used herein, the term “substantially free of” or “substantially inthe absence of” refers to a nucleoside composition that includes atleast 85 or 90% by weight, preferably 95% to 98% by weight, and evenmore preferably 99% to 100% by weight, of the designated enantiomer ofthat nucleoside. In a preferred embodiment, in the methods and compoundsof this invention, the compounds are substantially free of enantiomers.

Similarly, the term “isolated” refers to a nucleoside composition thatincludes at least 85 or 90% by weight, preferably 95% to 98% by weight,and even more preferably 99% to 100% by weight, of the nucleoside, theremainder comprising other chemical species or enantiomers.

The term “alkyl,” as used herein, unless otherwise specified, refers toa saturated straight, branched, or cyclic, primary, secondary, ortertiary hydrocarbon of typically C₁ to C₁₀, and specifically includesmethyl, trifluoromethyl, ethyl, propyl, isopropyl, cyclopropyl, butyl,isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl,isohexyl, cyclohexyl, cyclohexylmethyl, 3-methylpentyl,2,2-dimethylbutyl, and 2,3-dimethylbutyl. The term includes bothsubstituted and unsubstituted alkyl groups. Alkyl groups can beoptionally substituted with one or more moieties selected from the groupconsisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy,nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, orphosphonate, or any other viable functional group that does not inhibitthe pharmacological activity of this compound, either unprotected, orprotected, as necessary, as known to those skilled in the art, forexample, as taught in T. W. Greene and P. G. M. Wuts, “Protective Groupsin Organic Synthesis,” 3rd ed., John Wiley & Sons, 1999, herebyincorporated by reference.

The term “lower alkyl,” as used herein, and unless otherwise specified,refers to a C₁ to C₄ saturated straight, branched, or if appropriate, acyclic (for example, cyclopropyl) alkyl group, including bothsubstituted and unsubstituted forms. Unless otherwise specificallystated in this application, when alkyl is a suitable moiety, lower alkylis preferred. Similarly, when alkyl or lower alkyl is a suitable moiety,unsubstituted alkyl or lower alkyl is preferred.

The terms “alkylamino” or “arylamino” refer to an amino group that hasone or two alkyl or aryl substituents, respectively.

The term “protected,” as used herein and unless otherwise defined,refers to a group that is added to an oxygen, nitrogen, or phosphorusatom to prevent its further reaction or for other purposes. A widevariety of oxygen and nitrogen protecting groups are known to thoseskilled in the art of organic synthesis. Non-limiting examples include:C(O)-alkyl, C(O)Ph, C(O)aryl, CH₃, CH₂-alkyl, CH₂-alkenyl, CH₂Ph,CH₂-aryl, CH₂O-alkyl, CH₂O-aryl, SO₂-alkyl, SO₂-aryl,tert-butyldimethylsilyl, tert-butyldiphenylsilyl, and1,3-(1,1,3,3-tetraisopropyldisiloxanylidene).

The term “aryl,” as used herein, and unless otherwise specified, refersto phenyl, biphenyl, or naphthyl, and preferably phenyl. The termincludes both substituted and unsubstituted moieties. The aryl group canbe substituted with one or more moieties selected from the groupconsisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy,nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, orphosphonate, either unprotected, or protected as necessary, as known tothose skilled in the art, for example, as taught in T. W. Greene and P.G. M. Wuts, “Protective Groups in Organic Synthesis,” 3rd ed., JohnWiley & Sons, 1999.

The terms “alkaryl” or “alkylaryl” refer to an alkyl group with an arylsubstituent. The terms “aralkyl” or “arylalkyl” refer to an aryl groupwith an alkyl substituent.

The term “halo,” as used herein, includes chloro, bromo, iodo andfluoro.

The term “acyl” refers to a carboxylic acid ester in which thenon-carbonyl moiety of the ester group is selected from straight,branched, or cyclic alkyl or lower alkyl, alkoxyalkyl includingmethoxymethyl, aralkyl including benzyl, aryloxyalkyl such asphenoxymethyl, aryl including phenyl optionally substituted with halogen(F, Cl, Br, I), C₁ to C₄ alkyl or C₁ to C₄ alkoxy, sulfonate esters suchas alkyl or aralkyl sulphonyl including methanesulfonyl, the mono, di ortriphosphate ester, trityl or monomethoxytrityl, substituted benzyl,trialkylsilyl (e.g. dimethyl-t-butylsilyl) or diphenylmethylsilyl. Arylgroups in the esters optimally comprise a phenyl group.

The term “lower acyl” refers to an acyl group in which the non-carbonylmoiety is lower alkyl.

The term “purine” or “pyrimidine” base includes, but is not limited to,adenine, N⁶-alkylpurines, N⁶-acylpurines (wherein acyl is C(O)(alkyl,aryl, alkylaryl, or arylalkyl), N⁶-benzylpurine, N⁶-halopurine,N⁶-vinylpurine, N⁶-acetylenic purine, N⁶-acyl purine, N⁶-hydroxyalkylpurine, N⁶-allylaminopurine, N⁶-thioallyl purine, N²-alkylpurines,N²-alkyl-6-thiopurines, thymine, cytosine, 5-fluorocytosine,5-methylcytosine, 6-azapyrimidine, including 6-azacytosine, 2- and/or4-mercaptopyrmidine, uracil, 5-halouracil, including 5-fluorouracil,C⁵-alkylpyrimidines, C⁵-benzylpyrimidines, C⁵-halopyrimidines,C⁵-vinylpyrimidine, C⁵-acetylenic pyrimidine, C⁵-acyl pyrimidine,C⁵-hydroxyalkyl purine, C⁵-amidopyrimidine, C⁵-cyanopyrimidine,C⁵-iodopyrimidine, C⁶-lodo-pyrimidine, C⁵-Br-vinyl pyrimidine,C⁶-Br-vinyl pyrimidine, C⁵-nitropyrimidine, C⁵-amino-pyrimidine,N²-alkylpurines, N²-alkyl-6-thiopurines, 5-azacytidinyl, 5-azauracilyl,triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, andpyrazolopyrimidinyl. Purine bases include, but are not limited to,guanine, adenine, hypoxanthine, 2,6-diaminopurine, and 6-chloropurine.Functional oxygen and nitrogen groups on the base can be protected asnecessary or desired. Suitable protecting groups are well known to thoseskilled in the art, and include trimethylsilyl, dimethylhexylsilyl,t-butyldimethylsilyl, and t-butyldiphenylsilyl, trityl, alkyl groups,and acyl groups such as acetyl and propionyl, methanesulfonyl, andp-toluenesulfonyl.

The term “acyl” or “O-linked ester” refers to a group of the formulaC(O)R′, wherein R′ is an straight, branched, or cyclic alkyl (includinglower alkyl), amino acid, aryl including phenyl, ailcaryl, aralkylincluding benzyl, alkoxyalkyl including methoxymethyl, aryloxyalkyl suchas phenoxymethyl; or substituted ailcyl (including lower alkyl), arylincluding phenyl optionally substituted with chloro, bromo, fluoro,iodo, C₁ to C₄ alkyl or C₁ to C₄ alkoxy, sulfonate esters such as alkylor aralkyl sulphonyl including methanesulfonyl, the mono, di ortriphosphate ester, trityl or monomethoxy-trityl, substituted benzyl,alkaryl, aralkyl including benzyl, alkoxyalicyl including methoxymethyl,aryloxyalkyl such as phenoxymethyl. Aryl groups in the esters optimallycomprise a phenyl group. In particular, acyl groups include acetyl,trifluoroacetyl, methylacetyl, cyclopropylacetyl, cyclopropyl carboxy,propionyl, butyryl, hexanoyl, heptanoyl, octanoyl, neo-heptanoyl,phenylacetyl, 2-acetoxy-2-phenylacetyl, diphenylacetyl,α-methoxy-α-trifluoromethyl-phenylacetyl, bromoacetyl,2-nitro-benzeneacetyl, 4-chloro-benzeneacetyl,2-chloro-2,2-diphenylacetyl, 2-chloro-2-phenylacetyl, trimethylacetyl,chlorodifluoroacetyl, perfluoroacetyl, fluoroacetyl,bromodifluoroacetyl, methoxyacetyl, 2-thiopheneacetyl,chlorosulfonylacetyl, 3-methoxyphenylacetyl, phenoxyacetyl,tert-butylacetyl, trichloroacetyl, monochloro-acetyl, dichloroacetyl,7H-dodecafluoro-heptanoyl, perfluoro-heptanoyl,7H-dodeca-fluoroheptanoyl, 7-chlorododecafluoro-heptanoyl,7-chloro-dodecafluoro-heptanoyl, 7H-dodecafluoroheptanoyl,7H-dodeca-fluoroheptanoyl, nona-fluoro-3,6-dioxa-heptanoyl,nonafluoro-3,6-dioxaheptanoyl, perfluoroheptanoyl, methoxybenzoyl,methyl 3-amino-5-phenylthiophene-2-carboxyl,3,6-dichloro-2-methoxy-benzoyl, 4-(1,1,2,2-tetrafluoro-ethoxy)-benzoyl,2-bromo-propionyl, omega-aminocapryl, decanoyl, n-pentadecanoyl,stearyl, 3-cyclopentyl-propionyl, 1-benzene-carboxyl, O-acetylmandelyl,pivaloyl acetyl, 1-adamantane-carboxyl, cyclohexane-carboxyl,2,6-pyridinedicarboxyl, cyclopropane-carboxyl, cyclobutane-carboxyl,perfluorocyclohexyl carboxyl, 4-methylbenzoyl, chloromethyl isoxazolylcarbonyl, perfluorocyclohexyl carboxyl, crotonyl,1-methyl-1H-indazole-3-carbonyl, 2-propenyl, isovaleryl,1-pyrrolidinecarbonyl, 4-phenylbenzoyl. When the term acyl is used, itis meant to be a specific and independent disclosure of acetyl,trifluoroacetyl, methylacetyl, cyclopropylacetyl, propionyl, butyryl,hexanoyl, heptanoyl, octanoyl, neo-heptanoyl, phenylacetyl,diphenylacetyl, ct-trifluoromethyl-phenylacetyl, bromoacetyl,4-chloro-benzeneacetyl, 2-chloro-2,2-diphenylacetyl,2-chloro-2-phenylacetyl, trimethylacetyl, chlorodifluoroacetyl,perfluoroacetyl, fluoroacetyl, bromodifluoroacetyl, 2-thiopheneacetyl,tert-butylacetyl, trichloroacetyl, monochloro-acetyl, dichloroacetyl,methoxybenzoyl, 2-bromo-propionyl, decanoyl, n-pentadecanoyl, stearyl,3-cyclopentyl-propionyl, 1-benzene-carboxyl, pivaloyl acetyl,1-adamantane-carboxyl, cyclohexane-carboxyl, 2,6-pyridinedicarboxyl,cyclopropane-carboxyl, cyclobutane-carboxyl, 4-methylbenzoyl, crotonyl,1-methyl-1H-indazole-3-carbonyl, 2-propenyl, isovaleryl,4-phenylbenzoyl.

The term “amino acid” includes naturally occurring and synthetic α, β γor δ amino acids, and includes but is not limited to, amino acids foundin proteins, i.e. glycine, alanine, valine, leucine, isoleucine,methionine, phenylalanine, tryptophan, proline, serine, threonine,cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine,arginine and histidine. In a preferred embodiment, the amino acid is inthe L-configuration. Alternatively, the amino acid can be a derivativeof alanyl, valinyl, leucinyl, isoleucinyl, prolinyl, phenylalaninyl,tryptophanyl, methioninyl, glycinyl, serinyl, threoninyl, cysteinyl,tyrosinyl, asparaginyl, glutaminyl, aspartoyl, glutaroyl, lysinyl,argininyl, histidinyl, β-alanyl, β-valinyl, β-leucinyl, β-isoleucinyl,β-prolinyl, β-phenylalaninyl, β-tryptophanyl, β-methioninyl, β-glycinyl,β-serinyl, β-threoninyl, β-cysteinyl, β-tyrosinyl, β-asparaginyl,β-glutaminyl, β-aspartoyl, β-glutaroyl, β-lysinyl, β-argininyl orβ-histidinyl. When the term amino acid is used, it is considered to be aspecific and independent disclosure of each of the esters of α, β γ or δglycine, alanine, valine, leucine, isoleucine, methionine,phenylalanine, tryptophan, proline, serine, threonine, cysteine,tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginineand histidine in the D and L-configurations.

The term “host,” as used herein, refers to a unicellular ormulticellular organism in which the virus can replicate, including celllines and animals, and preferably a human. Alternatively, the host canbe carrying a part of the viral genome, whose replication or functionscan be altered by the compounds of the present invention. The term hostspecifically refers to infected cells, cells transfected with all orpart of the viral genome, and animals, in particular, primates andhumans. In most animal applications of the present invention, the hostis a human patient. Veterinary applications, in certain indications,however, are clearly anticipated by the present invention.

The term “pharmaceutically acceptable salt or prodrug” is usedthroughout the specification to describe any pharmaceutically acceptableform (such as an ester, phosphate ester, salt of an ester or a relatedgroup) of a compound which, upon administration to a patient, providesthe active compound. Pharmaceutically acceptable salts include thosederived from pharmaceutically acceptable inorganic or organic bases andacids. Suitable salts include those derived from alkali metals such aspotassium and sodium, alkaline earth metals such as calcium andmagnesium, among numerous other acids well known in the pharmaceuticalart. Pharmaceutically acceptable prodrugs refer to a compound that ismetabolized, for example hydrolyzed or oxidized, in the host to form thecompound of the present invention. Typical examples of prodrugs includecompounds that have biologically labile protecting groups on afunctional moiety of the active compound. Prodrugs include compoundsthat can be oxidized, reduced, aminated, deaminated, hydroxylated,dehydroxylated, hydrolyzed, dehydrolyzed, alkylated, dealkylated,acylated, deacylated, phosphorylated, dephosphorylated to produce theactive compound.

I. Active Compound, and Physiologically Acceptable Derivatives and SaltsThereof

A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside or itspharmaceutically acceptable salt or prodrug thereof is provided of thestructure:

-   -   wherein Base refers to a naturally occurring or modified purine        or pyrimidine base; X is O, S, CH₂, Se, NH, N-alkyl, CHW, C(W)₂,        wherein W is F, Cl, Br, or I;    -   R¹ and R⁷ are independently H, phosphate, including        monophosphate, diphosphate, triphosphate, or a stabilized        phosphate prodrug, H-phosphonate, including stabilized        H-phosphonates, acyl, including optionally substituted phenyl        and lower acyl, alkyl, including lower alkyl, O-substituted        carboxyalkylamino or its peptide derivatives, sulfonate ester,        including alkyl or arylalkyl sulfonyl, including methanesulfonyl        and benzyl, wherein the phenyl group is optionally substituted,        a lipid, including a phospholipid, an L or D-amino acid, a        carbohydrate, a peptide, a cholesterol, or other        pharmaceutically acceptable leaving group which when        administered in vivo is capable of providing a compound wherein        R¹ is H or phosphate; R² is OH or phosphate; R¹ and R² or R⁷ can        also be linked with cyclic phosphate group; and    -   R² and R^(2′) are independently H, C₁₋₄ alkyl, C₁₋₄ alkenyl,        C₁₋₄ alkynyl, vinyl, N₃, CN, Cl, Br, F, I, NO₂, C(O)O(C₁₋₄        alkyl), C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄ alkynyl), C(O)O(C₁₋₄        alkenyl), O(C₁₋₄ acyl), O(C₁₋₄ alkyl), O(C₁₋₄ alkenyl), S(C₁₋₄        acyl), S(C₁₋₄ alkyl), S(C₁₋₄ alkynyl), S(C₁₋₄ alkenyl), SO(C₁₋₄        acyl), SO(C₁₋₄ alkyl), SO(C₁₋₄ alkynyl), SO(C₁₋₄ alkenyl),        SO₂(C₁₋₄ acyl), SO₂(C₁₋₄ alkyl), SO₂(C₁₋₄ alkynyl), SO₂(C₁₋₄        alkenyl), O₃S(C₁₋₄ acyl), O₃S(C₁₋₄ alkyl), O₃S(C₁₋₄ alkenyl),        NH₂, NH(C₁₋₄ alkyl), NH(C₁₋₄ alkenyl), NH(C₁₋₄ alkynyl), NH(C₁₋₄        acyl), N(C₁₋₄ alkyl)₂, N(C₁₋₁₈ acyl)₂, wherein alkyl, alkynyl,        alkenyl and vinyl are optionally substituted by N₃, CN, one to        three halogen (Cl, Br, F, I), NO₂, C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄        alkyl), C(O)O(C₁₋₄ alkynyl), C(O)O(C₁₋₄ alkenyl), O(C₁₋₄ acyl),        O(C₁₋₄ alkyl), O(C₁₋₄ alkenyl), S(C₁₋₄ acyl), S(C₁₋₄ alkyl),        S(C₁₋₄ alkynyl), S(C₁₋₄ alkenyl), SO(C₁₋₄ acyl), SO(C₁₋₄ alkyl),        SO(C₁₋₄ alkynyl), SO(C₁₋₄ alkenyl), SO₂(C₁₋₄ acyl), SO₂(C₁₋₄        alkyl), SO₂(C₁₋₄ alkynyl), SO₂(C₁₋₄ alkenyl), O₃S(C₁₋₄ acyl),        O₃S(C₁₋₄ alkyl), O₃S(C₁₋₄ alkenyl), NH₂, NH(C₁₋₄ alkyl), NH(C₁₋₄        alkenyl), NH(C₁₋₄ alkynyl), NH(C₁₋₄ acyl), N(C₁₋₄ alkyl)₂,        N(C₁₋₄ acyl)₂, OR⁷, R² and R^(2′) can be linked together to form        a vinyl optionally substituted by one or two of N₃, CN, Cl, Br,        F, I, NO₂; and    -   R⁶ is an optionally substituted alkyl (including lower alkyl),        cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH),        fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃,        CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro.

In a second embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof isprovided of the structure:

-   -   wherein Base, R¹, R², R^(2′), R⁶ and R⁷ are as defined above.

A third embodiment provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof ofthe structure:

-   -   wherein X, R¹, R², R^(2′), R⁶ and R⁷ are as defined above, and    -   Base is selected from

-   -   Y is N or CH;    -   R³, R⁴ and R⁵ are independently H, halogen (including F, Cl, Br,        I), OH, OR′, SH, SR′, NH₂, NHR′, NR′₂, lower alkyl of C₁-C₆,        halogenated (F, Cl, Br, I) lower alkyl of C₁-C₆ such as CF₃ and        CH₂CH₂F, lower alkenyl of C₂-C₆ such as CH═CH₂, halogenated (F,        Cl, Br, I) lower alkenyl of C₂-C₆ such as CH═CHCl, CH═CHBr and        CH═CHI, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, Cl,        Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C₁-C₆ such as        CH₂OH and CH₂CH₂OH, halogenated (F, Cl, Br, I) lower alkoxy of        C₁-C₆, CO₂H, CO₂R′, CONH₂, CONHR′, CONR′₂, CH═CHCO₂H,        CH═CHCO₂R′;    -   R′ is an optionally substituted alkyl of C₁-C₁₂ (particularly        when the alkyl is an amino acid residue), cycloalkyl, optionally        substituted alkynyl of C₂-C₆, optionally substituted lower        alkenyl of C₂-C₆, or optionally substituted acyl.

In a fourth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof isprovided of the structure:

-   -   wherein Base is selected from

-   -   and, wherein R¹, R², R^(2′), R³, R⁴, R⁵, R⁶ and Y are as defined        above.

A fifth embodiment provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof ofthe structure:

-   -   wherein Base refers to a naturally occurring or modified purine        or pyrimidine base;    -   R⁷ is independently H, phosphate, including monophosphate,        diphosphate, triphosphate, or a stabilized phosphate prodrug,        H-phosphonate, including stabilized H-phosphonates, acyl,        including optionally substituted phenyl and lower acyl, alkyl,        including lower alkyl, O-substituted carboxyalkylamino or its        peptide derivatives, sulfonate ester, including alkyl or        arylalkyl sulfonyl, including methanesulfonyl and benzyl,        wherein the phenyl group is optionally substituted, a lipid,        including a phospholipid, an L or D-amino acid, a carbohydrate,        a peptide, a cholesterol, or other pharmaceutically acceptable        leaving group which when administered in vivo is capable of        providing a compound wherein R¹ or R⁷ is independently H or        phosphate; R¹ and R⁷ can also be linked with cyclic phosphate        group; and    -   wherein X and R¹ are as defined above.

In a sixth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleosideor its pharmaceutically acceptable salt or prodrug thereof is providedof the structure:

-   -   wherein Base refers to a naturally occurring or modified purine        or pyrimidine base; and    -   wherein R¹ and R⁷ are as defined above.

A seventh embodiment provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof ofthe structure:

-   -   wherein Base is selected from

-   -   and wherein X, Y, R¹, R³, R⁴, R⁵, R⁷ and R′ are as defined        above.

In an eighth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof isprovided of the structure:

-   -   wherein Base is selected from

-   -   and, wherein Y, R¹, R³, R⁴, R⁵, R⁷ and R′ are as defined above.

A ninth embodiment provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof ofthe structure:

-   -   wherein Base is:

-   -   and wherein X is defined as above, R¹ is H, R² is OH, R²′ is H,        R³ is H, R⁴ is NH₂ or OH, and R⁶ is H.

In a tenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleosideor its pharmaceutically acceptable salt or prodrug thereof is providedof the structure:

-   -   wherein Base is:

-   -   and wherein R¹ is H, R² is OH, R^(2′) is H, R³ is H, R⁴ is NH₂        or OH, and R⁶ is H.

An eleventh embodiment provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof ofthe structure:

-   -   wherein Base is:

-   -   and wherein X is defined as above, R¹ is H, R³ is H, R⁴ is NH₂        or OH, R⁶ is H, and R⁷ is H.

In a twelfth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof isprovided of the structure:

-   -   wherein Base is:

-   -   and wherein R¹ is H, R³ is H, R⁴ is NH₂ or OH, and R⁷ is H.

A thirteenth embodiment provides a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside or its pharmaceutically acceptable salt or prodrug thereof ofthe structure:

In a fourteenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside, its pharmaceutically acceptable salt or product thereof isprovided by the structure:

-   -   wherein X, R¹, R⁶ and R⁷ are as defined above.

In a fifteenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside, its pharmaceutically acceptable salt or product thereof isprovided by the structure:

-   -   wherein R¹, R⁶ and R⁷ are as defined above.

In a sixteenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside nucleoside, its pharmaceutically acceptable salt or productthereof is provided by the structure:

In a seventeenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside, its pharmaceutically acceptable salt or product thereof isprovided by the structure:

-   -   wherein X and R¹ are as defined above.

In an eighteenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside, its pharmaceutically acceptable salt or product thereof isprovided by the structure:

In a nineteenth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside, its pharmaceutically acceptable salt or product thereof isprovided by the structure:

-   -   wherein X and R¹ are as defined above.

In a twentieth embodiment, a (2′R)-2′-deoxy-2′-fluoro-2′-C-methylnucleoside, its pharmaceutically acceptable salt or product thereof isprovided by the structure:

The present invention also contemplates 5′-triphosphate triphosphoricacid ester derivates of the 5′-hydroxyl group of a nucleoside compoundof the present invention having the following general structuralformula:

-   -   wherein Base, X, R², R^(2′), and R⁶ are as defined as above.

The compounds of the present invention are also intended to includepharmaceutically acceptable salts of the triphosphate ester as well aspharmaceutically acceptable salts of 5′-diphosphate and 5′-monophosphateester derivatives of the following structural formulas, respectively.

-   -   wherein Base, X, R², R^(2′) and R⁶ are as defined above.

Further non-limiting examples of phosphoric acid derivatives are thenucleosides of the present invention are shown below:

The present invention also contemplates that any phosphate nucleosidederivative can include a 5′-(S-acyl-2-thioethyl)phosphate or “SATE” monoor di-ester derivative of the 5′-monophosphates.

Alternative embodiments are also contemplated wherein the N-4 aminogroup on a phosphate nucleoside derivative can be replaced with H, F,Cl, Br or I.

Additional embodiments include 3′ and/or 5′ produrgs as described inmore detail herein.

In the various embodiments, the fluorinated derivatives are preferred.Fluorine is viewed as “isosteric” with hydrogen because of its size (Vander Waals radii for H is 1.20 A and for F 1.35 A). However, the atomicweight (18.998) and electronegativity of fluorine (4.0 [Pauling'sscale], 4.000 [Sanderson's scale]) are more similar to oxygen (3.5[Pauling]. 3.654 [Sanderson]) than hydrogen (2.1 [Pauling], 2.592[Sanderson]) (March, J., “Advances in Organic Chemistry Reactions,Mechanisms, and Structure” Third edition, 1985, p. 14., WileyInterscience, New York). Fluorine is known to be capable of forming ahydrogen bond, but unlike a hydroxyl group (which can act both as protonacceptor and proton donor) fluorine acts only as a proton acceptor. Onthe other hand, 2′-fluoro-ribonucleosides can be viewed as analogues ofboth ribonucleosides and deoxynucleosides. They may be better recognizedby viral RNA polymerase at the triphosphate level than by the host RNApolymerase thus selectively inhibiting the viral enzyme.

II. Pharmaceutically Acceptable Salts and Prodrugs

In cases where compounds are sufficiently basic or acidic to form stablenontoxic acid or base salts, administration of the compound as apharmaceutically acceptable salt may be appropriate. Pharmaceuticallyacceptable salts include those derived from pharmaceutically acceptableinorganic or organic bases and acids. Suitable salts include thosederived from alkali metals such as potassium and sodium, alkaline earthmetals such as calcium and magnesium, among numerous other acids wellknown in the pharmaceutical art. In particular, examples ofpharmaceutically acceptable salts are organic acid addition salts formedwith acids, which form a physiological acceptable anion, for example,tosylate, methanesulfonate, acetate, citrate, malonate, tartarate,succinate, benzoate, ascorbate, α-ketoglutarate, and α-glycerophosphate.Suitable inorganic salts may also be formed, including, sulfate,nitrate, bicarbonate, and carbonate salts.

Pharmaceutically acceptable salts may be obtained using standardprocedures well known in the art, for example by reacting a sufficientlybasic compound such as an amine with a suitable acid affording aphysiologically acceptable anion. Alkali metal (for example, sodium,potassium or lithium) or alkaline earth metal (for example calcium)salts of carboxylic acids can also be made.

Any of the nucleosides described herein can be administered as anucleotide prodrug to increase the activity, bioavailability, stabilityor otherwise alter the properties of the nucleoside. A number ofnucleotide prodrug ligands are known. In general, alkylation, acylationor other lipophilic modification of the mono, di or triphosphate of thenucleoside will increase the stability of the nucleotide. Examples ofsubstituent groups that can replace one or more hydrogens on thephosphate moiety are alkyl, aryl, steroids, carbohydrates, includingsugars, 1,2-diacylglycerol and alcohols. Many are described in R. Jonesand N. Bischofberger, Antiviral Research, 27 (1995) 1-17. Any of thesecan be used in combination with the disclosed nucleosides to achieve adesired effect.

The active nucleoside can also be provided as a 5′-phosphoether lipid ora 5′-ether lipid, as disclosed in the following references, which areincorporated by reference herein: Kucera, L. S., N. Iyer, E. Leake, A.Raben, Modest E. K., D. L. W., and C. Piantadosi. 1990. “Novelmembrane-interactive ether lipid analogs that inhibit infectious HIV-1production and induce defective virus formation.” AIDS Res. Hum. RetroViruses. 6:491-501; Piantadosi, C., J. Marasco C. J., S. L.Morris-Natschke, K. L. Meyer, F. Gumus, J. R. Surles, K. S. Ishaq, L. S.Kucera, N. Iyer, C. A. Wallen, S. Piantadosi, and E. J. Modest. 1991.“Synthesis and evaluation of novel ether lipid nucleoside conjugates foranti-HIV activity.” J. Med. Chem. 34:1408.1414; Hosteller, K. Y., D. D.Richman, D. A. Carson, L. M. Stuhmiller, G. M. T. van Wijk, and H. vanden Bosch. 1992. “Greatly enhanced inhibition of human immunodeficiencyvirus type 1 replication in CEM and HT4-6C cells by 3′-deoxythymidinediphosphate dimyristoylglycerol, a lipid prodrug of 3′-deoxythymidine.”Antimicrob. Agents Chemother. 36:2025.2029; Hosetler, K. Y., L. M.Stuhmiller, H. B. Lenting, H. van den Bosch, and D. D. Richman, 1990.“Synthesis and antiretroviral activity of phospholipid analogs ofazidothymidine and other antiviral nucleosides.” J. Biol. Chem.265:61127.

Nonlimiting examples of U.S. patents that disclose suitable lipophilicsubstituents that can be covalently incorporated into the nucleoside,preferably at the 5′-OH position of the nucleoside or lipophilicpreparations, include U.S. Pat. Nos. 5,149,794; 5,194,654; 5,223,263;5,256,641; 5,411,947; 5,463,092; 5,543,389; 5,543,390; 5,543,391; and5,554,728, all of which are incorporated herein by reference. Foreignpatent applications that disclose lipophilic substituents that can beattached to the nucleosides of the present invention, or lipophilicpreparations, include WO 89/02733, WO 90/00555, WO 91/16920, WO91/18914, WO 93/00910, WO 94/26273, WO 96/15132, EP 0 350 287, EP93917054.4, and WO 91/19721.

III. Pharmaceutical Compositions

Pharmaceutical compositions based upon a β-D or β-L compound disclosedherein or its pharmaceutically acceptable salt or prodrug can beprepared in a therapeutically effective amount for treating aFlaviviridae infection, including hepatitis C virus, West Nile Virus,yellow fever virus, and a rhinovirus infection, optionally incombination with a pharmaceutically acceptable additive, carrier orexcipient. The therapeutically effective amount may vary with theinfection or condition to be treated, its severity, the treatmentregimen to be employed, the pharmacokinetics of the agent used, as wellas the patient treated.

In one aspect according to the present invention, the compound accordingto the present invention is formulated preferably in a mixture with apharmaceutically acceptable carrier. In general, it is preferable toadminister the pharmaceutical composition in orally administrable form,but formulations may be administered via parenteral, intravenous,intramuscular, transdermal, buccal, subcutaneous, suppository or otherroute. Intravenous and intramuscular formulations are preferablyadministered in sterile saline. One of ordinary skill in the art maymodify the formulation within the teachings of the specification toprovide numerous formulations for a particular route of administrationwithout rendering the compositions of the present invention unstable orcompromising its therapeutic activity. In particular, a modification ofa desired compound to render it more soluble in water or other vehicle,for example, may be easily accomplished by routine modification (saltformulation, esterification, etc.).

In certain pharmaceutical dosage forms, the prodrug form of thecompound, especially including acylated (acetylated or other) and etherderivatives, phosphate esters and various salt forms of the presentcompounds, is preferred. One of ordinary skill in the art will recognizehow to readily modify the present compound to a prodrug form tofacilitate delivery of active compound to a targeted site within thehost organism or patient. The artisan also will take advantage offavorable pharmacokinetic parameters of the prodrug form, whereapplicable, in delivering the desired compound to a targeted site withinthe host organism or patient to maximize the intended effect of thecompound in the treatment of a Flaviviridae infection, includinghepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirusinfection.

The amount of compound included within therapeutically activeformulations, according to the present invention, is an effective amountfor treating the infection or condition, in preferred embodiments, aFlaviviridae infection, including hepatitis C virus, West Nile Virus,yellow fever virus, and a rhinovirus infection. In general, atherapeutically effective amount of the present compound inpharmaceutical dosage form usually ranges from about 50 mg to about2,000 mg or more, depending upon the compound used, the condition orinfection treated and the route of administration. For purposes of thepresent invention, a prophylactically or preventively effective amountof the compositions, according to the present invention, falls withinthe same concentration range as set forth above for therapeuticallyeffective amount and is usually the same as a therapeutically effectiveamount.

Administration of the active compound may range from continuous(intravenous drip) to several oral administrations per day (for example,Q.I.D., B.I.D., etc.) and may include oral, topical, parenteral,intramuscular, intravenous, subcutaneous, transdermal (which may includea penetration enhancement agent), buccal and suppository administration,among other routes of administration. Enteric-coated oral tablets mayalso be used to enhance bioavailability and stability of the compoundsfrom an oral route of administration. The most effective dosage formwill depend upon the pharmacokinetics of the particular agent chosen, aswell as the severity of disease in the patient. Oral dosage forms areparticularly preferred, because of ease of administration andprospective favorable patient compliance.

To prepare the pharmaceutical compositions according to the presentinvention, a therapeutically effective amount of one or more of thecompounds according to the present invention is preferably mixed with apharmaceutically acceptable carrier according to conventionalpharmaceutical compounding techniques to produce a dose. A carrier maytake a wide variety of forms depending on the form of preparationdesired for administration, e.g., oral or parenteral. In preparingpharmaceutical compositions in oral dosage form, any of the usualpharmaceutical media may be used. Thus, for liquid oral preparationssuch as suspensions, elixirs and solutions, suitable carriers andadditives including water, glycols, oils, alcohols, flavoring agents,preservatives, coloring agents and the like may be used. For solid oralpreparations such as powders, tablets, capsules, and for solidpreparations such as suppositories, suitable carriers and additivesincluding starches, sugar carriers, such as dextrose, mannitol, lactoseand related carriers, diluents, granulating agents, lubricants, binders,disintegrating agents and the like may be used. If desired, the tabletsor capsules may be enteric-coated for sustained release by standardtechniques. The use of these dosage forms may significantly impact thebioavailability of the compounds in the patient.

For parenteral formulations, the carrier will usually comprise sterilewater or aqueous sodium chloride solution, though other ingredients,including those that aid dispersion, also may be included. Where sterilewater is to be used and maintained as sterile, the compositions andcarriers must also be sterilized. Injectable suspensions may also beprepared, in which case appropriate liquid carriers, suspending agentsand the like may be employed.

Liposomal suspensions (including liposomes targeted to viral antigens)may also be prepared by conventional methods to produce pharmaceuticallyacceptable carriers. This may be appropriate for the delivery of freenucleosides, acyl nucleosides or phosphate ester prodrug forms of thenucleoside compounds according to the present invention.

In particularly preferred embodiments according to the presentinvention, the compounds and compositions are used to treat, prevent ordelay the onset of a Flaviviridae infection, including hepatitis Cvirus, West Nile Virus, yellow fever virus, and a rhinovirus infection.The present compounds are preferably administered orally, but may beadministered parenterally, topically or in suppository form.

The compounds according to the present invention, because of their lowtoxicity to host cells in certain instances, may be advantageouslyemployed prophylactically to prevent a Flaviviridae infection, includinghepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirusinfection or to prevent the occurrence of clinical symptoms associatedwith the viral infection or condition. Thus, the present invention alsoencompasses methods for the prophylactic treatment of viral infection,and in particular a Flaviviridae infection, including hepatitis C virus,West Nile Virus, yellow fever virus, and a rhinovirus infection. In thisaspect, according to the present invention, the present compositions areused to prevent or delay the onset of a Flaviviridae infection,including hepatitis C virus, West Nile Virus, yellow fever virus, and arhinovirus infection. This prophylactic method comprises administrationto a patient in need of such treatment, or who is at risk for thedevelopment of the virus or condition, an amount of a compound accordingto the present invention effective for alleviating, preventing ordelaying the onset of the viral infection or condition. In theprophylactic treatment according to the present invention, it ispreferred that the antiviral compound utilized should be low in toxicityand preferably non-toxic to the patient. It is particularly preferred inthis aspect of the present invention that the compound that is usedshould be maximally effective against the virus or condition and shouldexhibit a minimum of toxicity to the patient. In the case of aFlaviviridae infection, including hepatitis C virus, West Nile Virus,yellow fever virus, and a rhinovirus infection, compounds according tothe present invention, which may be used to treat these disease states,may be administered within the same dosage range for therapeutictreatment (i.e., about 250 micrograms up to 1 gram or more from one tofour times per day for an oral dosage form) as a prophylactic agent toprevent the proliferation of the viral infection, or alternatively, toprolong the onset of the viral infection, which manifests itself inclinical symptoms.

In addition, compounds according to the present invention can beadministered in combination or alternation with one or more antiviralagents, including other compounds of the present invention. Certaincompounds according to the present invention may be effective forenhancing the biological activity of certain agents according to thepresent invention by reducing the metabolism, catabolism or inactivationof other compounds and as such, are co-administered for this intendedeffect.

IV. Stereoisomerism and Polymorphism

It is appreciated that nucleosides of the present invention have severalchiral centers and may exist in and be isolated in optically active andracemic forms. Some compounds may exhibit polymorphism. It is to beunderstood that the present invention encompasses any racemic, opticallyactive, diastereomeric, polymorphic, or stereoisomeric form, or mixturesthereof, of a compound of the invention, which possess the usefulproperties described herein. It being well known in the art how toprepare optically active forms (for example, by resolution of theracemic form by recrystallization techniques, by synthesis fromoptically-active starting materials, by chiral synthesis, or bychromatographic separation using a chiral stationary phase).

Carbons of the nucleoside are chiral, their nonhydrogen substituents(the base and the CHOR groups, respectively) can be either cis (on thesame side) or trans (on opposite sides) with respect to the sugar ringsystem. The four optical isomers therefore are represented by thefollowing configurations (when orienting the sugar moiety in ahorizontal plane such that the oxygen atom is in the back): cis (withboth groups “up”, which corresponds to the configuration of naturallyoccurring β-D nucleosides), cis (with both groups “down”, which is anonnaturally occurring β-L configuration), trans (with the C2′substituent “up” and the C4′ substituent “down”), and trans (with theC2′ substituent “down” and the C4′ substituent “up”). The“D-nucleosides” are cis nucleosides in a natural configuration and the“L-nucleosides” are cis nucleosides in the nonnaturally occurringconfiguration.

Likewise, most amino acids are chiral (designated as L or D, wherein theL enantiomer is the naturally occurring configuration) and can exist asseparate enantiomers.

Examples of methods to obtain optically active materials are known inthe art, and include at least the following.

-   -   i) physical separation of crystals—a technique whereby        macroscopic crystals of the individual enantiomers are manually        separated. This technique can be used if crystals of the        separate enantiomers exist, i.e., the material is a        conglomerate, and the crystals are visually distinct;    -   ii) simultaneous crystallization—a technique whereby the        individual enantiomers are separately crystallized from a        solution of the racemate, possible only if the latter is a        conglomerate in the solid state;    -   iii) enzymatic resolutions—a technique whereby partial or        complete separation of a racemate by virtue of differing rates        of reaction for the enantiomers with an enzyme;    -   iv) enzymatic asymmetric synthesis—a synthetic technique whereby        at least one step of the synthesis uses an enzymatic reaction to        obtain an enantiomerically pure or enriched synthetic precursor        of the desired enantiomer;    -   v) chemical asymmetric synthesis—a synthetic technique whereby        the desired enantiomer is synthesized from an achiral precursor        under conditions that produce asymmetry (i.e., chirality) in the        product, which may be achieved using chiral catalysts or chiral        auxiliaries;    -   vi) diastereomer separations—a technique whereby a racemic        compound is reacted with an enantiomerically pure reagent (the        chiral auxiliary) that converts the individual enantiomers to        diastereomers. The resulting diastereomers are then separated by        chromatography or crystallization by virtue of their now more        distinct structural differences and the chiral auxiliary later        removed to obtain the desired enantiomer;    -   vii) first- and second-order asymmetric transformations—a        technique whereby diastereomers from the raceniate equilibrate        to yield a preponderance in solution of the diastereomer from        the desired enantiomer or where preferential crystallization of        the diastereomer from the desired enantiomer perturbs the        equilibrium such that eventually in principle all the material        is converted to the crystalline diastereomer from the desired        enantiomer. The desired enantiomer is then released from the        diastereomer;    -   viii) kinetic resolutions—this technique refers to the        achievement of partial or complete resolution of a racemate (or        of a further resolution of a partially resolved compound) by        virtue of unequal reaction rates of the enantiomers with a        chiral, non-racemic reagent or catalyst under kinetic        conditions;    -   ix) enantiospecific synthesis from non-racemic precursors—a        synthetic technique whereby the desired enantiomer is obtained        from non-chiral starting materials and where the stereochemical        integrity is not or is only minimally compromised over the        course of the synthesis;    -   x) chiral liquid chromatography—a technique whereby the        enantiomers of a racemate are separated in a liquid mobile phase        by virtue of their differing interactions with a stationary        phase. The stationary phase can be made of chiral material or        the mobile phase can contain an additional chiral material to        provoke the differing interactions;    -   xi) chiral gas chromatography—a technique whereby the racemate        is volatilized and enantiomers are separated by virtue of their        differing interactions in the gaseous mobile phase with a column        containing a fixed non-racemic chiral adsorbent phase;    -   xii) extraction with chiral solvents—a technique whereby the        enantiomers are separated by virtue of preferential dissolution        of one enantiomer into a particular chiral solvent;    -   xiii) transport across chiral membranes—a technique whereby a        racemate is placed in contact with a thin membrane barrier. The        barrier typically separates two miscible fluids, one containing        the racemate, and a driving force such as concentration or        pressure differential causes preferential transport across the        membrane barrier. Separation occurs as a result of the        non-racemic chiral nature of the membrane which allows only one        enantiomer of the racemate to pass through.        Chiral chromatography, including simulated moving bed        chromatography, is used in one embodiment. A wide variety of        chiral stationary phases are commercially available.

Some of the compounds described herein contain olefinic double bonds andunless otherwise specified, are meant to include both E and Z geometricisomers.

In addition, some of the nucleosides described herein, may exist astautomers, such as, keto-enol tautomers. The individual tautomers aswell as mixtures thereof are intended to be encompassed within thecompounds of the present invention as illustrated below.

A (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine:

A (2′R)-2′-deoxy-2′-fluoro-2′-C-methylguanosine:

A (2′R)-2-amino-2′-deoxy-2′-fluoro-2′-C-methyladenosine:

In each example above, the first drawn structure is the preferred form.

V. Prodrugs and Derivatives

The active compound can be administered as any salt or prodrug that uponadministration to the recipient is capable of providing directly orindirectly the parent compound, or that exhibits activity itself.Nonlimiting examples are the pharmaceutically acceptable salts(alternatively referred to as “physiologically acceptable salts”), and acompound, which has been alkylated, acylated, or otherwise modified atthe 5′-position, or on the purine or pyrimidine base (a type of“pharmaceutically acceptable prodrug”). Further, the modifications canaffect the biological activity of the compound, in some cases increasingthe activity over the parent compound. This can easily be assessed bypreparing the salt or prodrug and testing its antiviral activityaccording to the methods described herein, or other methods known tothose skilled in the art.

Pharmaceutically Acceptable Salts

In cases where compounds are sufficiently basic or acidic to form stablenontoxic acid or base salts, administration of the compound as apharmaceutically acceptable salt may be appropriate. Examples ofpharmaceutically acceptable salts are organic acid addition salts formedby addition of acids, which form a physiological acceptable anion, forexample, tosylate, methanesulfonate, acetate, citrate, malonate,tartarate, succinate, benzoate, ascorate, a-ketoglutarate,a-glycerophosphate, formate, fumarate, propionate, glycolate, lactate,pyruvate, oxalate, maleate, and salicylate. Suitable inorganic salts mayalso be formed, including, sulfate, nitrate, bicarbonate, carbonatesalts, hydrobromate and phosphoric acid. In a preferred embodiment, thesalt is a mono- or di-hydrochloride salt.

Pharmaceutically acceptable salts may be obtained using standardprocedures well known in the art, for example by reacting a sufficientlybasic compound such as an amine with a suitable acid affording aphysiologically acceptable anion. Alkali metal (for example, sodium,potassium or lithium) or alkaline earth metal (for example calcium)salts of carboxylic acids can also be made. In one embodiment, the saltis a hydrochloride, hydrobromide, or mesylate salt of the compound. Inanother embodiment, the pharmaceutically acceptable salt is adihydrochloride, dihydrobromide, or dimesylate salt.

Nucleotide Prodrug Formulations

The nucleosides described herein can be administered as a nucleotideprodrug to increase the activity, bioavailability, stability orotherwise alter the properties of the nucleoside. A number of nucleotideprodrug ligands are known. In general, alkylation, acylation or otherlipophilic modification of the mono-, di- or triphosphate of thenucleoside reduces polarity and allows passage into cells. Examples ofsubstituent groups that can replace one or more hydrogens on thephosphate moiety are ailcyl, aryl, steroids, carbohydrates, includingsugars, 1,2-diacylglycerol and alcohols. Many are described in R. Jonesand N. Bisehoferger, Antiviral Research, 1995, 27:1-17. Any of these canbe used in combination with the disclosed nucleosides to achieve adesired effect.

In an alternative embodiment, the nucleoside is delivered as aphosphonate or a SATE derivative.

The active nucleoside can also be provided as a 2′-, 3′- and/or5′-phosphoether lipid or a 2′-, 3′- and/or 5′-ether lipid. Non-limitingexamples are described include the following references, which areincorporated by reference herein: Kucera, L. S., N. Iyer, E. Leake, A.Raben, Modest E. K., D. L. W., and C. Piantadosi. 1990. “Novelmembrane-interactive ether lipid analogs that inhibit infectious HIV-1production and induce defective virus formation.” AIDS Res. Hum. RetroViruses. 6:491-501; Piantadosi, C., J. Marasco C. J., S. L.Morris-Natschke, K. L. Meyer, F. Gumus, J. R. Surles, K. S. Ishaq, L. S.Kucera, N. Iyer, C A. Wallen, S. Piantadosi, and E. J. Modest. 1991.“Synthesis and evaluation of novel ether lipid nucleoside conjugates foranti-HIV activity.” J. Med. Chem. 34:1408.1414; Hosteller, K. Y., D. D.Richman, D. A. Carson, L. M. Stuhmiller, G. M. T. van Wijk, and H. vanden Bosch. 1992. “Greatly enhanced inhibition of human immunodeficiencyvirus type 1 replication in CEM and HT4-6C cells by 3′-deoxythyminediphosphate dimyristoylglycerol, a lipid prodrug of 3-deoxythymine.”Antlnzicrob. Agents Chemother. 36:2025.2029; Hosetler, K. Y., L. M.Stuhmiller, H. B. Lenting, H. van den Bosch, and D. D. Richman, 1990.“Synthesis and antiretroviral activity of phospholipid analogs ofazidothymidine and other antiviral nucleosides.” J. Biol. Chem.265:61127.

Nonlimiting examples of U.S. patents that disclose suitable lipophilicsubstituents that can be covalently incorporated into the nucleoside,preferably at the 2′-, 3′- and/or 5′-OH position of the nucleoside orlipophilic preparations, include U.S. Pat. Nos. 5,149,794 (Sep. 22,1992, Yatvin et al.); 5,194,654 (Mar. 16, 1993, Hostetler et al.,5,223,263 (Jun. 29, 1993, Hostetler et al.); 5,256,641 (Oct. 26, 1993,Yatvin et al.); 5,411,947 (May 2, 1995, Hostetler et al.); 5,463,092(Oct. 31, 1995, Hostetler et al.); 5,543,389 (Aug. 6, 1996, Yatvin etal.); 5,543,390 (Aug. 6, 1996, Yatvin et al.); 5,543,391 (Aug. 6, 1996,Yatvin et al.); and 5,554,728 (Sep. 10, 1996; Basava et al.), all ofwhich are incorporated herein by reference. Foreign patent applicationsthat disclose lipophilic substituents that can be attached to thenucleosides of the present invention, or lipophilic preparations,include WO 89/02733, WO 90/00555, WO 91/16920, WO 91/18914, WO 93/00910,WO 94/26273, WO 96/15132, EP 0350287, EP 93917054.4, and WO 91/19721.

Aryl esters, especially phenyl esters, are also provided. Nonlimitingexamples are disclosed in DeLambert et al., J. Med. Chem. 37: 498(1994). Phenyl esters containing a carboxylic ester ortho to thephosphate are also provided. Khaninei and Torrence, J. Med. Chem.;39:41094115 (1996). In particular, benzyl esters, which generate theparent compound, in some cases using substituents at the ortho- orpara-position to accelerate hydrolysis, are provided. Examples of thisclass of prodrugs are described by Mitchell et al., J. Chem. Soc. PerkinTrans. 12345 (1992); Brook, et al. WO 91/19721; and Glazier et al. WO91/1 9721.

Cyclic and noncyclic phosphonate esters are also provided. Nonlimitingexamples are disclosed in Hunston et al., J. Med. Chem. 27: 440-444(1984) and Starrett et al. J. Med. Chem. 37: 1857-1864 (1994).Additionally, cyclic 3′,5′-phosphate esters are provided. Nonlimitingexamples are disclosed in Meier et al. J. Med. Chem. 22: 811-815 (1979).Cyclic 1′,3′-propanyl phosphonate and phosphate esters, such as onescontaining a fused aryl ring, i.e. the cyclosaligenyl ester, are alsoprovided (Meier et al., Bioorg. Med. Chem. Lett. 7: 99-104 (1997)).Unsubstituted cyclic 1′,3′-propanyl esters of the monophosphates arealso provided (Farquhar et al., J. Med. Chem. 26: 1153 (1983); Farquharet al., J. Med. Chem. 28: 1358 (1985)) were prepared. In addition,cyclic 1′,3′-propanyl esters substituted with a pivaloyloxy methyloxygroup at C-1′ are provided (Freed et al., Biochem. Pharmac. 38: 3193(1989); Biller et al., U.S. Pat. No. 5,157,027).

Cyclic phosphoramidates are known to cleave in vivo by an oxidativemechanism. Therefore, in one embodiment of the present invention, avariety of substituted 1′,3′ propanyl cyclic phosphoramidates areprovided. Non-limiting examples are disclosed by Zon, Progress in Med.Chem. 19, 1205 (1982). Additionally, a number of 2′- and 3′-substitutedproesters are provided. 2′-Substituents include methyl, dimethyl, bromo,trifluoromethyl, chloro, hydroxy, and methoxy; 3′-substituents includingphenyl, methyl, trifluoromethyl, ethyl, propyl, i-propyl, andcyclohexyl. A variety of 1′-substituted analogs are also provided.

Cyclic esters of phosphorus-containing compounds are also provided.Non-limiting examples are described in the following:

-   -   di and tri esters of phosphoric acids as reported in Nifantyev        et al., Phosphorus, Sulfur Silicon and Related Elements, 113: 1        (1996); Wijnberg et al., EP-180276 A1;    -   phosphorus (III) acid esters. Kryuchkov et al., Izy. Akad. Nauk        SSSR, Ser. Khim. 6:1244 (1987). Some of the compounds were        claimed to be useful for the asymmetric synthesis of L-Dopa        precursors. Sylvain et al., DE3S 12781 A1;    -   phosphoramidates. Shili et al., Bull. Inst. Chem. Acad. Sin, 41:        9 (1994); Edmundson et al., J. Chem. Res. Synop. 5:122 (1989);        and    -   phosphonates. Neidlein et al., Heterocycles 35: 1185 (1993).        N⁴-acyl Prodrugs

The invention also provides N⁴-acyl prodrugs. A non-limiting example ofan N⁴-acyl derivative of (2′R)-2′-F-2′-C-methylcytidine is shown below:

-   -   wherein R can be any acyl group as described herein.

The invention also contemplates other embodiments, wherein the prodrugof a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L)includes biologically cleavable moieties at the 3′ and/or 5′ positions.Preferred moieties are natural of synthetic D or L amino acid esters,including D or L-valyl, though preferably L-amino acids esters, such asL-valyl, and alkyl esters including acetyl. Therefore, this inventionspecifically includes 3′-L or D-amino acid ester and 3′,5′-L orD-diamino acid ester of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside(β-D or β-L) nucleosides, preferably L-amino acid, with any desiredpurine or pyrimidine base, wherein the parent drug optionally has anEC₅₀ of less than 15 micromolar, and even more preferably less than 10micromolar; 3′-(alkyl or aryl) ester or 3′,5′-L-di(alkyl or aryl) esterof (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L) with anydesired purine or pyrimidine base, wherein the parent drug optionallyhas an EC₅₀ of less than 10 or 15 micromolar; and prodrugs of3′,5′-diesters of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleosides (β-Dor β-L) wherein (i) the 3′ ester is an amino acid ester and the 5′-esteris an alkyl or aryl ester; (ii) both esters are amino acid esters; (iii)both esters are independently alkyl or aryl esters; and (iv) the 3′ester is independently an alkyl or aryl ester and the 5′-ester is anamino acid ester, wherein the parent drug optionally has an EC₅₀ of lessthan 10 or 15 micromolar.

Non-limiting examples of prodrugs falling within the invention are:

VI. Combination or Alternation Therapy

In another embodiment, for the treatment, inhibition, prevention and/orprophylaxis of any viral infection described herein, the active compoundor its derivative or salt can be administered in combination oralternation with another antiviral agent. In general, in combinationtherapy, effective dosages of two or more agents are administeredtogether, whereas during alternation therapy, an effective dosage ofeach agent is administered serially. The dosage will depend onabsorption, inactivation and excretion rates of the drug as well asother factors known to those of skill in the art. It is to be noted thatdosage values will also vary with the severity of the condition to bealleviated. It is to be further understood that for any particularsubject, specific dosage regimens and schedules should be adjusted overtime according to the individual need and the professional judgment ofthe person administering or supervising the administration of thecompositions.

It has been recognized that drug-resistant variants of flaviviruses,pestiviruses or HCV can emerge after prolonged treatment with anantiviral agent. Drug resistance most typically occurs by mutation of agene that encodes for an enzyme used in viral replication. The efficacyof a drug against the viral infection can be prolonged, augmented, orrestored by administering the compound in combination or alternationwith a second, and perhaps third, antiviral compound that induces adifferent mutation from that caused by the principle drug.Alternatively, the pharmacokinetics, biodistribution or other parameterof the drug can be altered by such combination or alternation therapy.In general, combination therapy is typically preferred over alternationtherapy because it induces multiple simultaneous stresses on the virus.

For example, one skilled in the art will recognize that any antiviraldrug or therapy can be used in combination or alternation with anynucleoside of the present invention. Any of the viral treatmentsdescribed in the Background of the Invention can be used in combinationor alternation with the compounds described in this specification.Nonlimiting examples of the types of antiviral agents or their prodrugsthat can be used in combination with the compounds disclosed hereininclude: interferon, including interferon alpha 2a, interferon alpha 2b,a pegylated interferon, interferon beta, interferon gamma, interferontau and interferon omega; an interleukin, including interleukin 10 andinterleukin 12; ribavirin; interferon alpha or pegylated interferonalpha in combination with ribavirin or levovirin; levovirin; a proteaseinhibitor including an NS3 inhibitor, a NS3-4A inhibitor; a helicaseinhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5Bpolymerase inhibitor; gliotoxin; an IRES inhibitor; and antisenseoligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme;another nucleoside, nucleoside prodrug or nucleoside derivative; a1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene;amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; abenzenedicarboxamide; polyadenylic acid; a benzimidazoles; thymosin; abeta tubulin inhibitor; a prophylactic vaccine; an immune modulator, anIMPDH inhibitor; silybin-phosphatidylcholine phytosome; andmycophenolate.

Further nonlimiting examples of the types of drugs or their prodrugsdescribed above include: acyclovir (ACV), ganciclovir (GCV or DHPG) andits prodrugs (e.g. valyl-ganciclovir),E-5-(2-bromovinyl)-2′-deoxyuridine (BVDU),(E)-5-vinyl-1-β-D-arabonosyluracil (VaraU),(E)-5-(2-bromovinyl)-1-β-D-arabinosyluracil (BV-araU),1-(2-deoxy-2-fluoro-β-D-arabinosyl)-5-iodocytosine (D-FIAC),1-(2-deoxy-2-fluoro-β-L-arabinosyl)-5-methyluracil (L-FMAU, orclevudine), (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine[(S)-HPMPA],(S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)-2,6-diaminopurine[(S)-HPMPDAP], (S)-1-(3-hydroxy-2-phosphonyl-methoxypropyl)cytosine[(S)-HPMPC, or cidofivir], and(2S,4S)-1-[2-(hydroxymethyl)-1,3-dioxolan-4-yl]-5-iodouracil(L-5-IoddU), entecavir, lamivudine (3TC), LdT, LdC, tenofovir, andadefovir, the (−)-enantiomer of2-hydroxymethyl-5-(5-fluorocytosin-1-yl)-1,3-oxathiolane ((−)-FTC); the(−)-enantiomer of 2-hydroxymethyl-5-(cytosin-1-yl)-1,3-oxathiolane(3TC); carbovir, acyclovir, famciclovir, penciclovir, AZT, DDI, DDC,L-(−)-FMAU, D4T, amdoxovir, Reverset, Racivir, abacavir, L-DDA phosphateprodrugs, and β-D-dioxolanyl-6-chloropurine (ACP), non-nucleoside RTinhibitors such as nevirapine, MKC-442, DMP-226 (sustiva), proteaseinhibitors such as indinavir, saquinavir, Kaletra, atazanavir; andanti-HIV compounds such as BILN-2061, ISIS 14803; viramidine, NM 283,VX-497, JKT-003, levovirin, isatoribine, albuferon, Peg-infergen,VX-950, R803, HCV-086, R1479 and DMP45.

Pharmaceutical Compositions

Hosts, including humans, infected with pestivirus, flavivirus, HCVinfection, or any other condition described herein, or another organismreplicating through a RNA-dependent RNA viral polymerase, or fortreating any other disorder described herein, can be treated byadministering to the patient an effective amount of the active compoundor a pharmaceutically acceptable prodrug or salt thereof in the presenceof a pharmaceutically acceptable carrier or dilutent. The activematerials can be administered by any appropriate route, for example,orally, parenterally, intravenously, intradermally, subcutaneously, ortopically, in liquid or solid form.

A preferred dose of the compound for a Flaviviridae infection, includinghepatitis C virus, West Nile Virus and yellow fever virus and rhinovirusinfection will be in the range from about 50 to about 2000 mg one tofour times per day. Lower doses may be useful, and thus ranges caninclude from 50-1,000 mg one to four times per day. The effective dosagerange of the pharmaceutically acceptable salts and prodrugs can becalculated based on the weight of the parent nucleoside to be delivered.If the salt or prodrug exhibits activity in itself the effective dosagecan be estimated as above using the weight of the salt or prodrug, or byother means known to those skilled in the art.

The compound is conveniently administered in unit any suitable dosageform, including but not limited to one containing 25 to 3000 mg,preferably 50 to 2000 mg of active ingredient per unit dosage form. Anoral dosage of 50-1000 mg is usually convenient, including in one ormultiple dosage forms of 50, 100, 200, 250, 300, 400, 500, 600, 700,800, 900 or 1000 mgs. Also contemplated are doses of 0.1-50 mg, or0.1-20 mg or 0.1-10.0 mg. Furthermore, lower doses may be utilized inthe case of administration by a non-oral route, as, for example, byinjection or inhalation.

Ideally the active ingredient should be administered to achieve peakplasma concentrations (C_(max)) of the active compound of from about 5.0to 70 μM, preferably about 5.0 to 15 μM. This may be achieved, forexample, by the intravenous injection of a 0.1 to 5% solution of theactive ingredient, optionally in saline, or administered as a bolus ofthe active ingredient.

The concentration of active compound in the drug composition will dependon absorption, inactivation and excretion rates of the drug as well asother factors known to those of skill in the art. It is to be noted thatdosage values will also vary with the severity of the condition to bealleviated. It is to be further understood that for any particularsubject, specific dosage regimens should be adjusted over time accordingto the individual need and the professional judgment of the personadministering or supervising the administration of the compositions, andthat the concentration ranges set forth herein are exemplary only andare not intended to limit the scope or practice of the claimedcomposition. The active ingredient may be administered at once, or maybe divided into a number of smaller doses to be administered at varyingintervals of time.

A preferred mode of administration of the active compound is oral. Oralcompositions will generally include an inert diluent or an ediblecarrier. They may be enclosed in gelatin capsules or compressed intotablets. For the purpose of oral therapeutic administration, the activecompound can be incorporated with excipients and used in the form oftablets, troches, or capsules. Pharmaceutically compatible bindingagents, and/or adjuvant materials can be included as part of thecomposition.

The tablets, pills, capsules, troches and the like can contain any ofthe following ingredients, or compounds of a similar nature: a bindersuch as microcrystalline cellulose, gum tragacanth or gelatin; anexcipient such as starch or lactose, a disintegrating agent such asalginic acid, Primogel, or corn starch; a lubricant such as magnesiumstearate or Sterotes; a glidant such as colloidal silicon dioxide; asweetening agent such as sucrose or saccharin; or a flavoring agent suchas peppermint, methyl salicylate, or orange flavoring. When the dosageunit form is a capsule, it can contain, in addition to material of theabove type, a liquid carrier such as a fatty oil. In addition, dosageunit forms can contain various other materials which modify the physicalform of the dosage unit, for example, coatings of sugar, shellac, orother enteric agents.

The compound can be administered as a component of an elixir,suspension, syrup, wafer, chewing gum or the like. A syrup may contain,in addition to the active compounds, sucrose as a sweetening agent andcertain preservatives, dyes and colorings and flavors.

The compound or a pharmaceutically acceptable prodrug or salts thereofcan also be mixed with other active materials that do not impair thedesired action, or with materials that supplement the desired action,such as antibiotics, antifungals, anti-inflammatories, or otherantivirals, including other nucleoside compounds. Solutions orsuspensions used for parenteral, intradermal, subutaneous, or topicalapplication can include the following components: a sterile diluent suchas water for injection, saline solution, fixed oils, polyethyleneglycols, glycerine, propylene glycol or other synthetic solvents;antibacterial agents such as benzyl alcohol or methyl parabens;antioxidants such as ascorbic acid or sodium bisulfite; chelating agentssuch as ethylenediaminetetraacetic acid; buffers such as acetates,citrates or phosphates and agents for the adjustment of tonicity such assodium chloride or dextrose. The parental preparation can be enclosed inampoules, disposable syringes or multiple dose vials made of glass orplastic.

If administered intravenously, preferred carriers are physiologicalsaline or phosphate buffered saline (PBS).

In a preferred embodiment, the active compounds are prepared withcarriers that will protect the compound against rapid elimination fromthe body, such as a controlled release formulation, including implantsand microencapsulated delivery systems. Biodegradable, biocompatiblepolymers can be used, such as ethylene vinyl acetate, polyanhydrides,polyglycolic acid, collagen, polyorthoesters and polylactic acid.Methods for preparation of such formulations will be apparent to thoseskilled in the art. The materials can also be obtained commercially fromAlza Corporation.

Liposomal suspensions (including liposomes targeted to infected cellswith monoclonal antibodies to viral antigens) are also preferred aspharmaceutically acceptable carriers. These may be prepared according tomethods known to those skilled in the art. For example, liposomeformulations may be prepared by dissolving appropriate lipid(s) (such asstearoyl phosphatidyl ethanolamine, stearoyl phosphatidyl choline,arachadoyl phosphatidyl choline, and cholesterol) in an inorganicsolvent that is then evaporated, leaving behind a thin film of driedlipid on the surface of the container. An aqueous solution of the activecompound or its monophosphate, diphosphate, and/or triphosphatederivatives is then introduced into the container. The container is thenswirled by hand to free lipid material from the sides of the containerand to disperse lipid aggregates, thereby forming the liposomalsuspension.

VII. Biological Methods

Antiviral Testing of Candidate Compounds with HCV Replicon System inHuh7 Cells.

Huh7 cells harboring the HCV replicon can be cultivated in DMEM media(high glucose, no pyruvate) containing 10% fetal bovine serum, 1×non-essential Amino Acids, Pen-Strep-Glu (100 units/liter, 100microgram/liter, and 2.92 mg/liter, respectively) and 500 to 1000microgram/milliliter G418. Antiviral screening assays can be done in thesame media without G418 as follows: in order to keep cells inlogarithmic growth phase, cells are seeded in a 96-well plate at lowdensity, for example 1000 cells per well. The test compound is addedimmediately after seeding the cells and incubate for a period of 3 to 7days at 37° C. in an incubator. Media is then removed, and the cells areprepared for total nucleic acid extraction (including replicon RNA andhost RNA). Replicon RNA can then be amplified in a Q-RT-PCR protocol,and quantified accordingly. The observed differences in replicon HCV RNAlevels compared to the untreated control is one way to express theantiviral potency of the test compound.

In another typical setting, a compound might reduce the viral RNApolymerase activity, but not the host RNA polymerase activity.Therefore, quantification of rRNA or beta-actin mRNA (or any other hostRNA fragment) and comparison with RNA levels of the no-drug control is arelative measurement of the inhibitory effect of the test compound oncellular RNA polymerases.

Phosphorylation Assay of Nucleoside to Active Triphosphate

To determine the cellular metabolism of the compounds, Huh-7 cells areobtained from the American Type Culture Collection (Rockville, Md.), andare grown in 225 cm² tissue culture flasks in minimal essential mediumsupplemented with non-essential amino acids, 1% penicillin-streptomycin.The medium is renewed every three days, and the cells are sub culturedonce a week. After detachment of the adherent monolayer with a 10 minuteexposure to 30 mL of trypsin-EDTA and three consecutive washes withmedium, confluent Huh-7 cells are seeded at a density of 2.5×10⁶ cellsper well in a 6-well plate and exposed to 10 μM of [³H] labeled activecompound (500 dpm/pmol) for the specified time periods. The cells aremaintained at 37° C. under a 5% CO₂ atmosphere. At the selected timepoints, the cells are washed three times with ice-coldphosphate-buffered saline (PBS). Intracellular active compound and itsrespective metabolites are extracted by incubating the cell pelletovernight at −20° C. with 60% methanol followed by extraction with anadditional 20 μL of cold methanol for one hour in an ice bath. Theextracts are then combined, dried under gentle filtered air flow andstored at −20° C. until HPLC analysis.

Bioavailability Assay in Cynomolgus Monkeys

Within 1 week prior to the study initiation, the cynomolgus monkey issurgically implanted with a chronic venous catheter and subcutaneousvenous access port (VAP) to facilitate blood collection and underwent aphysical examination including hematology and serum chemistryevaluations and the body weight was recorded. Each monkey (six total)receives approximately 250 μCi of ³H-labeled compound combined with eachdose of active compound at a dose level of 10 mg/kg at a doseconcentration of 5 mg/mL, either via an intravenous bolus (3 monkeys,IV), or via oral gavage (3 monkeys, PO). Each dosing syringe is weighedbefore dosing to gravimetrically determine the quantity of formulationadministered. Urine samples are collected via pan catch at thedesignated intervals (approximately 18-0 hours pre-dose, 0-4, 4-8 and8-12 hours post-dosage) and processed. Blood samples are collected aswell (pre-dose, 0.25, 0.5, 1, 2, 3, 6, 8, 12 and 24 hours post-dosage)via the chronic venous catheter and VAP or from a peripheral vessel ifthe chronic venous catheter procedure should not be possible. The bloodand urine samples are analyzed for the maximum concentration (C_(max)),time when the maximum concentration is achieved (T_(max)), area underthe curve (AUC), half life of the dosage concentration (T_(1/2)),clearance (CL), steady state volume and distribution (V_(ss)) andbioavailability (F).

Bone Marrow Toxicity Assay

Human bone marrow cells are collected from normal healthy volunteers andthe mononuclear population are separated by Ficoll-Hypaque gradientcentrifugation as described previously by Sommadossi J-P, Carlisle R.“Toxicity of 3′-azido-3′-deoxythymidine and9-(1,3-dihydroxy-2-propoxymethyl)guanine for normal human hematopoieticprogenitor cells in vitro” Antimicrobial Agents and Chemotherapy 1987;31:452-454; and Sommadossi J-P, Schinazi R F, Chu C K, Xie M-Y.“Comparison of cytotoxicity of the (−)- and (+)-enantiomer of2′,3′-dideoxy-3′-thiacytidine in normal human bone marrow progenitorcells” Biochemical Pharmacology 1992; 44:1921-1925. The culture assaysfor CFU-GM and BFU-E are performed using a bilayer soft agar ormethylcellulose method. Drugs are diluted in tissue culture medium andfiltered. After 14 to 18 days at 37° C. in a humidified atmosphere of 5%CO₂ in air, colonies of greater than 50 cells are counted using aninverted microscope. The results are presented as the percent inhibitionof colony formation in the presence of drug compared to solvent controlcultures.

Mitochondria Toxicity Assay

Fifty microliters of 2× drug dilutions were added per well in a 96 wellplate. A “no drug” (media only) control was used to determine maximumamount of mitochondrial DNA produced and ribosomal DNA. 3TC @ 10 μM wasused as a negative control, and ddC @ 10 μM was used as a toxic control.Ribosomal DNA levels were used to determine specific toxicity tomitochondria or generally cytotoxicity. HepG2 cells (5,000 cells/well at50 μl) were added to the plate. The plate was incubated at 37° C. in ahumidified 5% CO₂ atmosphere for 7 days. After incubation, thesupernatant was removed and stored for lactic acid quantification, andtotal DNA was extracted from cells as described in the RNeasy 96handbook (February 1999), pages 22-23. No DNA digestions were performed,therefore total RNA and DNA were extracted.

The extracted DNA was amplified and the change in mitochondrial DNA andribosomal DNA for each sample was determined. The fold difference inmitochondrial DNA normalized for ribosomal DNA relative to control wascalculated.

Lactic acid quantification was performed by the D-Lactic Acid/L-Lacticacid test kit (Boehringer Mannheim/R-Biopharm/Roche). The total amountof lactic acid produced for each sample was found as well as the foldchange in lactic acid production (% of lactic acid/% of rDNA) asdescribed in the manufacturers instructions.

Cytotoxicity Assay

50 μl of 2× drug dilutions were added per well in a 96 well plate. Finalconcentrations of drug ranged from 1 to 100 μM. A “no drug” (media only)control was used to determine the minimum absorbance values and a“cells+media only” control was used for maximum absorbance value. Asolvent control was also used. Cells were then added (PBM: 5×10⁴cells/well; CEM: 2.5×10³ cells/well; Vero, HepG2, Huh-7, and Clone A:5×10³ cells/well) and incubated at 37° C. in a humidified 5% CO₂atmosphere for 3-5 days (PBM: 5 days; CEM: 3 days, all others: 4 days).After incubation, 20 μl of MTS dye was added from Cell Titer Aqueous OneSolution Cell Proliferation Assay to each well and the plate wasre-incubated for 2-4 hours. The absorbance (490 nm) was then read on anELISA plate reader using the media only/no cell wells as blanks. Percentinhibition was found and used to calculate the CC₅₀.

In Vivo Toxicity in Mice

In vivo toxicity was also determined following injections into femaleSwiss mice of the various nucleosides declosed in the present invention.Intraperitenal injections were given on days 0, day 1, day 2, day 3, andday 5 of varying doses of the particular nucleoside. Separate animalswere injected with vehicle as control groups. In these studies, eachdosing group contained 5-10 mice. The average weight change in each ofthe mice was measured as a sign of toxicity of the compound.

(BVDV) Yield Reduction Assay]

Madin-Darby Bovine Kidney (MDBK) cells were grown in Dulbecco's modifiedeagle medium supplemented with 10% horse serum and 100 μg/mlpenicillin-streptomycin. Cells were seeded in a 96-well plate at 5×10³cells/well and incubated for 72 h at 37° C. in a humidified 5% CO₂atmosphere. Cells were infected with either cytopathic (NADL strain) ornoncytopathic (SD-1 strain) BVDV at a virus dilution of 10⁻² andincubated for 45 min. Cell monolayers were washed three times withmedium. Fresh medium-containing test compounds in dose responseconcentrations or ribavirn, as a positive control, were added tocultures and medium containing no drug was added to the no-drugcontrols. After 72 h incubation, supernatant was collected and viral RNAwas extracted using the QIAmp Viral RNA Mini Kit (Qiagen, CA). Viralload was determined by Q-RT-PCR using primers specific for either NADLor SD-1 (1).

VIII. Synthetic Protocol

The following non-limiting embodiments illustrate some generalmethodologies to obtain the nucleosides of the present invention. Tworepresentative general methods for the preparation of compounds of thepresent invention are outlined in Schemes 1 and 2 while more specificexamples of these general methods are provided in Scheme 3 (Example 1),Scheme 4 (Example 2), Scheme 5 (Example 3), and Scheme 6 (Example 4).Scheme 1 represents a generalized process starting from a (2R)2-deoxy-2-methyl-2-fluoro-carbohydrate and forms the nucleosides of thepresent invention by condensing with a nucleobase. Scheme 2 starts froma pre-formed, purine or pyrimidine nucleoside, optionally substituted atC-4′ and constructs the C-2′ (R) methyl, fluoro nucleosides of thepresent invention. While these schemes illustrate the syntheses ofcompounds of the present invention of general formulas (I) and (II)wherein there is a furanose ring in the β-D-ribo configuration, this isnot intended to be a limitation on the scope of the process invention inany way, and they should not be so construed. Those skilled in the artof nucleoside and nucleotide synthesis will readily appreciate thatknown variations of the conditions and processes of the followingpreparative procedures and known manipulations of the nucleobase can beused to prepare these and other compounds of the present invention.Additionally, the L-enantiomers corresponding to the compounds of theinvention can be prepared following the same methods, beginning with thecorresponding L-carbohydrate building block or nucleoside L-enantiomeras the starting material.

1. Glycosylation of the Nucleobase with an Appropriately Modified Sugar

Step 1 in Scheme 1 introduces the 2-methyl group by using an appropriatealkylating agent such as methyllithium, trimethylaluminum, ormethylmagnesium bromide in an anhydrous solvent such as tetrahydrofuran(THF), chloroform, or diethyl ether. Compounds 1-1 through 1-4 can bepurely α or β or they may exist as an anomeric mixture containing both αand β anomers in any ratio. However, the preferred anomericconfiguration of structure 1-1 is β.

Step 2 introduces the fluorine atom at the 2-position of the alkylfuranoside. This can be achieved by treatment of the tertiary alcohol,1-2, with a commercially available fluorinating reagent such as(diethylamino)sulfur trifluoride (DAST) or Deoxofluor in an anhydrous,aprotic solvent such as tetrahydrofuran, chloroform, dichloromethane, ortoluene. Preferably the stereochemistry proceeds with inversion ofconfiguration at C-2. That is, starting from a C-2 hydroxyl “up” (orarabinofuranoside) in structure 1-2, the C-2 fluorine is “down” in theintermediate ribofuranoside 1-3.

In step 3, the optional protecting groups (Pg) can be deprotected andreprotected to groups more suitable for the remaining manipulations (T.W. Greene and P. G. M. Wuts, “Protective Groups in Organic Synthesis,”3rd ed., John Wiley & Sons, 1999). For example, benzyl ethers (Bn) maybe difficult to remove in the protected nucleoside, 1-5 and may bedeprotected and replaced with a group more facile to remove from thenucleoside of structural type 1-5. Furthermore, the anomeric position(C-1) can also be optionally manipulated to a suitable group for thecoupling reaction with the nucleobase (step 4). Several methods foranomeric manipulations are established to those skilled in the art ofnucleoside synthesis. Some non-limiting examples by treatment of thealkyl furanoside (1-3, R=alkyl) with a mixture of acetic anhydride,acetic acid, and a catalytic amount of sulfuric acid (acetolysis) toprovide structure 1-4 where R=Ac, with optional protecting groups. Also,the alkyl group in 1-3 may be converted to an acetate, benzoate,mesylate, tosylate, triflate, or tosylate, for example, by firsthydrolyzing the 1-Oalkyl group to a 1-hydroxyl group by using a mineralacid consisting of but not limited to sulfuric acid, hydrochloric acid,and hydrobromic acid or an organic acid consisting of but not limited totrifluoroacetic acid, acetic acid, and formic acid (at ambienttemperature or elevated temperature). The reducing sugar could then beconverted to the desired carbohydrate by treatment with acetyl chloride,acetic anhydride, benzoyl chloride, benzoic anhydride, methanesulfonylchloride, triflic anhydride, trifyl chloride, or tosyl chloride in thepresence of a suitable base such as triethylamine, pyridine, ordimethylaminopyridine.

The nucleosidic linkage is constructed by treatment of intermediate 1-3or 1-4 with the appropriate persilylated nucleobase in the presence of alewis acid such as tin tetrachloride, titanium tetrachloride,trimethylsilyltriflate, or a mercury (II) reagent (HgO/HgBr₂) usually atan elevated temperature in an aprotic solvent such as toluene,acetonitrile, benzene, or a mixture of any or all of these solvents.

The optional protecting groups in the protected nucleosides orstructural formula 1-5 can be cleaved following established deprotectionmethodologies (T. W. Greene and P. G. M. Wuts, “Protective Groups inOrganic Synthesis,” 3rd ed., John Wiley & Sons, 1999).

2. Modification of a Pre-Formed Nucleoside

The starting material for this process is an appropriately substitutedpurine or pyrimidine nucleoside with a 2′-OH and 2′-H. The nucleosidecan be purchased or can be prepared by any known means includingstandard coupling techniques. The nucleoside can be optionally protectedwith suitable protecting groups, preferably with acyl or silyl groups,by methods well known to those skilled in the art, as taught by T. W.Greene and P. G. M. Wuts, “Protective Groups in Organic Synthesis,” 3rded., John Wiley & Sons, 1999.

The purine or pyrimidine nucleoside can then be oxidized at the2′-position with the appropriate oxidizing agent in a compatible solventat a suitable temperature to yield the 2′-modified nucleoside. Possibleoxidizing agents are a mixture of dimethylsulfoxide, trifluoroaceticanhydride or acetic anhydride (a Swern/Moffat oxidation), chromiumtrioxide or other chromate reagent, Dess-Martin periodinane, or byruthenium tetroxide/sodium periodate.

The optionally protected nucleoside 2′-ketone is then alkylated usingsuch alkylating agents methyllithium, trimethylaluminum, methylmagnesiumbromide, or similar reagents in an anhydrous solvent suchtetrahydrofuran (THF), chloroform, or diethyl ether usually attemperatures below 0° C. Compounds of the structural formula 2-3 arepreferred to have the 2′(S) or 2′-methyl “down”, 2′-OH “up”configuration.

The nucleoside of structure 2-3 can be deprotected and reprotected witha number of protecting groups such as an O-acyl (alkyl or aryl),O-sulfonyl, or an N-acyl (alkyl or aryl) for the base. This optionalreprotection step need not be limited to protecting groups that functionas chemical protecting groups. Other protecting groups such as longchain acyl groups of between 6 and 18 carbon units or amino acids can beintroduced independently on the nucleobase or the sugar. The protectinggroups can serve as prodrugs of the active substance.

Step 5 introduces the fluorine atom at the 2′ position of the pre-formednucleoside. This can be achieved by treatment of the tertiary alcohol,2-4, with a commercially available fluorinating reagent such as(diethylamino)sulfur trifluoride (DAST) or Deoxofluor in an anhydrous,aprotic solvent such as tetrahydrofuran, chloroform, dichloromethane, ortoluene. Preferably the stereochemistry proceeds with inversion ofconfiguration at the 2′ position. That is, starting from a C-2′ hydroxyl“up” (or arabinonucleoside) in structure 2-4, the C-2′ flourine is“down” in the intermediate nucleoside 2-5. The absolute configuration ofa nucleoside of structure 2-4 is (2′S) while the absolute configurationof a nucleoside of structure 2-5 is (2′R).

Subsequently, the nucleosides of structural type 2-5 can be deprotectedby methods well known to those skilled in the art, as taught by T. W.Greene and P. G. M. Wuts, “Protective Groups in Organic Synthesis,” 3rded., John Wiley & Sons, 1999.

The following working examples provide a further understanding of themethod of the present invention and further exemplify the generalexamples in Schemes 1 and 2 above. These examples are of illustrativepurposes, and are not meant to limit the scope of the invention.Equivalent, similar or suitable solvents, reagents or reactionconditions may be substituted for those particular solvents, reagents orreaction conditions described without departing from the general scopeof the method.

EXAMPLES Example 1 Synthesis of(2′R)-2′-Deoxy-2′-Fluoro-2′-C-Methylcytidine Starting from aCarbohydrate

Step 1: Compound 3-1 (7.7 g, 0.022 mmol) was dissolved in anhydrousdiethyl ether and cooled to −78° C. To this solution was added MeLi (30mL, 1.6 M in diethyl ether). After the reaction was complete, themixture was treated with ammonium chloride (1 M, 65 mL) and the organicphase was separated, dried (Na₂SO₄), filtered, and concentrated todryness. Silica gel chromatography followed by crystallization fromdiethyl ether-hexanes afforded pure compound 3-2 (6.31 g). ¹H NMR (400MHz, CDCl₃): δ 1.40 (s, 3H), 3.41 (s, 3H), 3.49 (dd, 1H, J=10.3, 6.89Hz), 3.57 (dd, 1H, J=10.3, 3.88 Hz), 3.84 (d, 1H, J=7.3 Hz), 4.03 (m,1H), 4.48 (s, 1H), 4.58 (m, 3H), 4.83 (d, 1H, J=11.6 Hz), 7.31-7.36 (m,10H); ¹³C NMR (100 MHz, CDCl₃): δ 18.4, 55.4, 72.2, 73.4, 79.5, 80.2,84.7, 107.4, 127.7, 127.8, 127.83, 128.5, 138.2, 138.3.

Step 2: Compound 3-2 was dissolved in CH₂Cl₂ and was treated with DAST(4.0 mL, 30.3 mmol) at room temperature. The solution was stirred atroom temp overnight. The so-obtained mixture was poured into sat NaHCO₃(100 mL) and washed with sat NaHCO₃ (1×15 mL). The organic layer wasfurther worked up in the usual manner. Silica gel:chromatography (1:5EtOAc-hexanes) gave crude compound 3-3 (0.671 g) that was sufficientlypure for the next step. ¹H NMR (400 MHz, CDCl₃): δ 1.43 (d, 3H, J=22.8Hz), 3.35 (s, 3H), 3.49 (dd, 1H, J=10.5, 5.4 Hz), 3.55 (dd, 1H, J=10.5,4.1 Hz), 3.87 (dd, 1H, J=23.5, 7.5 Hz), 4.26 (m, 1H), 4.56 (d, 2H, J=6.9Hz), 4.66 (d, 2H, J=8.2 Hz), 4.72 (d, 1H, J=10.8 Hz), 7.29-7.36 (m,10H); ¹³C NMR (100 MHz, CDCl₃): δ 17.0 (d, J=24.4 Hz), 55.2, 77.1, 73.4,73.8, 77.3, 80.3, 81.2 (d, J=16 Hz), 99.7 (d, J=178.9 Hz), 106.8 (d,J=32.0 Hz), 127.7, 127.8, 128.1, 128.3, 128.5, 128.6, 137.8, 138.3; ¹⁹FNMR (100 MHz, CDCl₃): δ −8.2 (m, 1F).

Step 3: Compound 3-3 (0.39 g, 1.1 mmol) was dissolved in 1:2 EtOH-EtOAcand treated with Pd/C (˜0.1 g) and cyclohexene (˜1 mL). The mixture washeated to reflux overnight and then filtered through celite. The solventwas removed in vacuo and the residue was dissolved in pyridine (˜5 mL).To this solution was added benzoyl chloride (0.22 mL, 1.83 mmol) and themixture was stirred at room temp overnight. The pyridine was removed invacuo and the residue was partitioned between CH₂Cl₂ and sat NaHCO₃(10.0 mL). The organic phase was dried (Na₂SO₄), filtered, and thesolution was concentrated to dryness. Column chromatography provided0.350 g of pure compound 3-4. ¹H NMR (400 MHz, CDCl₃): δ 1.53 (d, 3H,J=22.4 Hz), 3.39 (s, 3H), 4.46 (dd, 1H, J=11.6, 4.7 Hz), 4.58 (m, 1H),4.65 (dd, 1H, J=11.6, 3.9 Hz), 4.87 (d, 1H, J=9.9 Hz), 5.64 (dd, 2H,J=24.1, 7.8 Hz), 7.29-7.36 (m, 10H); ¹⁹F NMR (100 MHz, CDCl₃): δ −7.5(m, 1F).

Step 4: A solution of bis(trimethylsilyl)-N-benzoylcytosine (0.28 g,0.77 mmol) and compound 3-4 (0.20 g, 0.5 mmol) in 1,2 dichloroethane (2mL) and toluene (2 mL) was treated with TMSOTf (0.15 mL, 0.77 mmol).After most of the starting material disappeared as judged by TLC, thesolution was cooled to room temp, washed with water (1×5 mL), brine (1×5mL), dried (Na₂SO₄), filtered, and concentrated to dryness. Flashchromatography followed by crystallization from CH₂Cl₂-hexanes affordedcompound 3-5 (68 mg). mp 241° C.; ¹H NMR (400 MHz, CDCl₃): δ 1.49 (d,3H, J=22.4 Hz), 4.64 (dd, 1H, J=12.9, 3.4 Hz), 4.73 (app d, 1H, J=9.5Hz), 4.89 (dd, 1H, J=12.7, 2.2 Hz), 5.56 (dd, 1H, J=20.7, 8.6 Hz), 6.52(d, 1H, J=15.9 Hz), 7.38-7.67 (m, 10H), 7.89 (d, 2H, J=6.9 Hz),8.07-8.11 (m, 5H), 8.67 (s, 1H); ¹⁹F NMR (100 MHz, CDCl₃): δ 2.85 (m,1F).

Step 5: Compound 3-5 (40 mg, 0.05 mmol) was dissolved in methanolicammonia and stirred at room temp for 48 h. The solution was concentratedto dryness and chromatographed (SiO₂) eluting with 1:4 EtOH—CH₂Cl₂. Theyield was about 12 mg of pure(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine, 3-6. ¹H NMR (400 MHz,DMSO-d₆): δ 1.16 (d, 3H, J=22.0 Hz), 3.61 (dd, 1H, J=11.6, 5.2 Hz),3.60-3.83 (m, 3H, J=10.5, 5.4 Hz), 5.24 (s, 1H, exchangeable with D₂O),5.59 (s, 1H, exchangeable with D₂O), 5.71 (d, 1H, J=7.3 Hz), 6.08 (d,1H, J=19.0 Hz), 7.24 (d, 1H, J=17.7 Hz, exchangeable with D₂O), 7.87 (d,1H); ¹⁹F NMR (100 MHz, DMSO-d₆): δ 4.13 (m, 1F).

Example 2 Synthesis of (2′R)-2′-Deoxy-2′-Fluoro-2′-C-MethylcytidineStarting from Cytidine

Step 1: To a suspension of cytidine (100 g, 0.411 mol) in DMF (2.06 L)is added benzoic anhydride (102.4 g, 0.452 mol). The mixture was stirredat room temperature for 20 h. The DMF was removed in vacuo and theresidue was triturated with diethyl ether. The resulting solid wascollected by suction filtration and washed with diethyl ether (2×200mL). Further drying in vacuo at room temperature gave the N⁴ benzamide(140.6 g, 98.3%). A portion of this material (139.3 g, 0.401 mol) wasdissolved in anhydrous pyridine (1.2 L) and was treated with1,3-dichloro-1,1,3,3-tetraisopropyl-disiloxane (141.4 mL, 0.441 mol) atroom temp. The solution was stirred at room temperature overnight. Themixture was concentrated to near dryness in vacuo and coevaporated withtoluene (3×200 mL). The residue was treated with EtOAc (1.8 L) andwashed with HCl (2×200 mL, 0.05 N), NaHCO₃ (5%, 2×400 mL). The organiclayer was washed dried (Na₂SO₄), filtered, and evaporated to dryness.Compound 4-1 (256.5 g, >100%) was isolated as a white foam and usedwithout further purification.

Step 2: Compound 4-1 (236.5 g, 0.40 mol) was dissolved in dry THF (1.22L). Anhydrous dmso (180.8 mL, 2.1 mol) was added and the resultingsolution was cooled to between −20° C. and −15° C. Trifluoroaceticanhydride (90.6 mL, 0.64 mol) was added dropwise over 45 minutes and thesolution was stirred between −20° C. and −15° C. for 2 hrs after whichanhydrous triethylamine (223.5 mL, 1.6 mol) was added over 20 min. Thecrude reaction containing ketone 4-2 was dissolved in EtOAc (500 mL),and the resulting solution was washed with H₂O (3×400 mL), dried(Na₂SO₄) and the solvents were removed in vacuo to give a yellow solidthat was purified on a silica gel column eluting with a stepwisegradient of Et₂O (0-60%) in hexanes followed by a stepwise gradient ofEtOAc (50-100%) in hexanes. The crude ketone so-obtained (˜192 g) wascrystallized from petroleum ether to give ketone 4-2 (138.91 g, 57.5%from cytidine) as a white solid and 22 g of unreacted starting material,4-1, as a yellow solid.

Step 3: Compound 4-2 (48.57 g, 8.26 mmol) was dissolved in anhydroustoluene (˜400 mL) and the solvent was removed in vacuo with exclusion ofmoisture. The residue was then further dried in vacuo (oil pump) foranother 2 h. With strict exclusion of moisture, the residual foam wasdissolved in anhydrous diethyl ether (1.03 L) under argon. The resultingsolution was cooled to −78° C. under argon and MeLi (1.6 M, 258.0 mL,0.413 mol) was added dropwise via additional funnel. After the additionwas complete, the mixture was stirred for 2 h at −78° C. Aqueous 1 MNH₄Cl (500 mL) was added slowly. After warming to room temperature, themixture was washed with H₂O (2×500 mL), dried (Na₂SO₄), and thenconcentrated to dryness to give a brown foam (˜60 g, >100%).

The reaction was performed two more times using 37.62 g and 56.4 g ofcompound 4-2. The combined crude products (128.0 g, 0.212 mol) weredissolved in THF (1.28 L) and treated with concd HOAc (23 mL, 0.402mol). To the solution was added TBAF (384.0 mL, 1 M in THF). Thesolution was stirred at room temp for 0.75 h and the mixture was treatedwith silica gel (750 g) and concentrated to dryness. The powder wasplaced on a silica gel column packed in CH₂Cl₂. Elution with 1:7EtOH—CH₂Cl₂ afforded a dark waxy solid that was pre-adsorbed on silicagel (300 g) and chromatographed as before. Compound 4-3 (46.4 g, 53.0%from 4-2) was isolated as an off-white solid. ¹H NMR (DMSO-d₆): δ 1.20(s, 3H, CH₃), 3.62-3.69 (m, 2H), 3.73-3.78 (m, 2H), 5.19 (t, 1H, J=5.4Hz, OH-5′), 5.25 (s, 1H, OH-2′), 5.52 (d, 1H, J=5.0 Hz, OH-3′), 5.99 (s,1H, H-1′), 7.32 (d, 1H, J=5.8 Hz), 7.50 (Ψt, 2H, J=7.7 Hz), 7.62 (Ψt,1H, J=7.3 Hz), 8.00 (d, 2H, J=7.3 Hz), 8.14 (d, 1H, J=6.9 Hz), 11.22 (s,1H, NH). Anal. Calcd for C₁₇H₁₉N₃O₆.0.5H₂O: C, 55.13; H, 5.44; N, 11.35.Found: C, 55.21; H, 5.47; N, 11.33.

Step 4: Compound 4-3 (46.0 g, 0.13 mol) was dissolved in anhydrouspyridine and concentrated to dryness in vacuo. The resulting syrup wasdissolved in anhydrous pyridine under argon and cooled to 0° C. withstirring. The brown solution was treated with benzoyl chloride (30 mL,0.250 mol) dropwise over 10 min. The ice bath was removed and stirringcontinued for 1.5 h whereby TLC showed no remaining starting material.The mixture was quenched by the addition of water (5 mL) andconcentrated to dryness. The residue was dissolved in a minimal amountof CH₂Cl₂ and washed with satd NaHCO₃ (1×500 mL) and H₂O (1×500 mL). Theorganic phase was dried (Na₂SO₄) and filtered, concentrated to drynessand chromatographed on silica gel eluting with a stepwise gradient ofEtOAc-hexanes (25-60%) to provide compound 4-4 as yellow foam (48.5 g,67%). ¹H NMR (CDCl₃): δ 1.64 (s, 3H, CH₃), 4.50 (m, 1H, H-4), 4.78-4.85(m, 2H, H-5′,5a′), 5.50 (d, 1H, J=3.4 Hz, H-3′), 6.42 (s, 1H, H-1′),7.44-7.54 (m, 7H, Ar), 7.57-7.66 (m, 3H, Ar), 7.94 (d, 2H, J=7.8 Hz),8.05-8.09 (m, 4H, Ar), 8.21 (d, 1H, J=7.3 Hz). Anal. Calcd forC₃₁H₂₇N₃O₈: C, 65.37; H, 4.78; N, 7.38. Found: C, 65.59; H, 4.79; N,7.16.

Step 5: Compound 4-4 (7.50 g, 0.013 mol) was dissolved in anhydroustoluene (150 mL) under argon and cooled to −20° C. DAST (2.5 mL, 18.9mmol) was added slowly and the cooling bath was removed after theaddition was complete. Stirring was continued for 1 h and the mixturewas poured into satd NaHCO₃ (100 mL) and washed until gas evolutionceased. The organic phase was dried (Na₂SO₄), concentrated, and purifiedby silica gel chromatography eluting with 1:1 EtOAc-hexanes. Yield was1.22 g (16.3%) of pure 4-5 as a white solid. mp 241° C.(CH₂Cl₂-hexanes); ¹H NMR (CDCl₃): δ 1.49 (d, 3H, J=22.4 Hz, CH₃), 4.64(dd, 1H, J=3.44, 12.9 Hz, H-5′), 4.73 (d, 1H, J=9.5 Hz, H-4′), 4.90 (dd,1H, J=2.4, 12.7 Hz, H-5a′), 5.56 (dd, 1H, J=8.6, 20.7 Hz, H-3′), 6.52(d, 1H, J=18.0 Hz, H-1′), 7.47-7.57 (m, 7H, Ar), 7.62-7.71 (m, 3H, Ar),7.89 (d, 2H, J=6.9 Hz), 8.07-8.11 (m, 5H, Ar), 8.67 (bs, 1H, NH). ¹⁹FNMR (CDCl₃): δ 3.3 (m). Anal. Calcd for C₃₁H₂₆FN₃O₇.0.7H₂O: C, 63.74; H,4.72; N, 7.20. Found: C, 63.71; H, 4.54; N, 7.20.

Step 6: Compound 4-5 (6.30 g, 0.011 mol) was suspended in methanolicammonia (ca 7 N, 150 mL) and stirred at room temperature overnight. Thesolvent was removed in vacuo, co-evaporated with methanol (1×20 mL), andpre-adsorbed onto silica gel. The white powder was placed onto a silicagel column (packed in CHCl₃) and the column was eluted with 9% EtOH inCHCl₃, then 17% EtOH and finally 25% EtOH in CHCl₃. Concentration of thefractions containing the product, filtration through a 0.4 μm disk, andlyophilization from water afforded compound 4-6, 2.18 g (76%). ¹H NMR(DMSO-d₆): δ 1.17 (d, 3H, J=22.3 Hz, CH₃), 3.63 (dd, 1H, J=2.7, 13.7 Hz,H-5′), 3.70-3.84 (m, 3H, H-3′, H-4′, H-5a′), 5.24 (app s, 1H, OH-3′),5.60 (d, 1H, J=5.4 Hz, H-5′), 5.74 (d, 1H, J=7.71 Hz, H-5), 6.07 (d, 1H,J=18.9 Hz, H-1′), 7.31 (s, 1H, NH₂), 7.42 (s, 1H, NH₂), 7.90 (d, 1H,J=7.3 Hz, H-6). ¹⁹F NMR (DMSO-d₆): δ 2.60 (m). Anal. Calcd forC₁₀H₁₄FN₃O₄.1.4H₂O: C, 44.22; H, 5.95; N, 14.77. Found: C, 42.24; H,5.63; N, 14.54. Compound 4-6 (0.10 g, 0.386 mmol) was converted to thehydrochloride salt by dissolving in water (2 mL) and adjusting the pH toapproximately 3.0 with 1 M HCl. The water was removed in vacuo and theresidue was crystallized from aqueous EtOH to give 4-6 as thehydrochloride salt (71.0 mg). mp 243° C. (dec); ¹H NMR (DMSO-d₆): δ 1.29(d, 3H, J=22.6 Hz, CH₃), 3.65 (dd, 1H, J=2.3, 12.7 Hz, H-5′), 3.76-3.90(m, 3H, H-3′, H-4′, H-5a′), 5.96 (d, 1H, J=17.3 Hz, H-1′), 6.15 (d, 1H,J=7.9 Hz, H-5), 8.33 (d, 1H, J=7.9 Hz, H-6), 8.69 (s, 1.5H, NH), 9.78(s, 1.5H, NH). ¹⁹F NMR (DMSO-d₆): δ 1.69 (m). Anal. Calcd forC₁₀H₁₄FN₃O₄. HCl: C, 40.62; H, 5.11; N, 14.21. Found: C, 40.80; H, 5.09;N, 14.23.

Example 3 Synthesis of(2′R)-6-Chloro-2′-Deoxy-2′-Fluoro-2′-C-Methylpurine Starting from6-Chloropurine Riboside

Step 1: The nucleoside, 6-chloropurine riboside, (3.18 g, 11.09 mmol)was dissolved in anhydrous pyridine (300 mL) and was treated dropwisewith 1,3-dichloro-1,1,3,3-tetraisopropyl-disiloxane (4.08 mL, 12.75mmol) at 0° C. under an argon atmosphere. The solution was brought toroom temp and stirred overnight. The mixture was concentrated to neardryness in vacuo, dissolved in a minimal amount of chloroform, andwashed with HCl (100 mL, 0.05 N) and NaHCO₃ (5%, 100 mL). The organiclayer was dried (Na₂SO₄), filtered, and evaporated to dryness to affordcompound 5-1 as an amber glass (6.10 g, >100%) that was used withoutfurther purification. ¹H NMR (CDCl₃): δ 1.01-1.13 (m, 24H), 4.03-4.18(m, 3H), 4.58 (d, 1H, J=5.2 Hz), 5.01 (m, 1H), 6.07 (s, 1H), 8.31 (s,1H), 8.71 (s, 1H).

Step 2: Compound 5-1 (7.13 g, 13.47 mmol) was dissolved in dry THF (35mL). Anhydrous DMSO (5.11 mL, 72.06 mmol) was added and the resultingsolution was cooled to between −20° C. and −15° C. Trifluoroaceticanhydride (3.06 mL, 21.69 mmol) was added dropwise over 45 minutes andthe solution was stirred between −20° C. and −15° C. for 2 hrs afterwhich anhydrous triethylamine (8.08 mL, 57.92 mmol) was added over 20min. The crude reaction containing ketone 5-2 was dissolved in Et₂O (25mL), and the resulting solution was washed with H₂O (2×50 mL), dried(Na₂SO₄) and the solvents were removed in vacuo to give a yellow solidthat was purified on a silica gel column eluting with a stepwisestepwise gradient of 0-50% petroleum ether-diethyl ether affordedcompound 5-2 as a mixture with the corresponding geminal diol. The glasswas dissolved in CH₂Cl₂ and stirred over an excess of MgSO₄ for 36 h.The mixture, free from the geminal diol, was filtered, and evaporated todryness to afford compound 5-2 as an amber glass (7.0 g, 97%). ¹H NMR(CDCl₃): δ 1.01-1.13 (m, 24H), 4.09-4.22 (m, 3H), 5.55 (d, 1H, J=9.6Hz), 5.80 (s, 1H), 8.19 (s, 1H), 8.61 (s, 1H).

Step 3: A solution of compound 5-2 (7.0 g, 13.26 mmol) in anhydroustetrahydrofuran (45 mL) was cooled to −78° C. with stirring under anargon atmosphere. To the solution was added methylmagnesium bromide(15.85 mL, 3.0 M in ethyl ether) dropwise over a 30 min period. Afterstirring for an additional 3 h at −78° C., the reaction was quenched bythe careful addition of aqueous 1 M NH₄Cl (50.0 mL). After warming toroom temperature, the mixture was washed with H₂O (2×500 mL), dried(Na₂SO₄), and concentrated to dryness to give a brown foam (3.8 g) thatwas dissolved in tetrahydrofuran (50 mL) and treated with a solution ofTBAF (18.9 mL, 1 M solution in THF) and glacial acetic acid (0.85 mL) atroom temp. The solution was stirred at room temp for 2 h, concentratedto dryness, and purified by silica gel chromatography to give compound5-3 (2.0 g, 50%).

Step 4: Compound 5-3 (0.491 g, 1.63 mmol) was dissolved in pyridine (3mL) and treated with acetic anhydride (0.38 mL, 4.08 mL) at room temp.The solution was stirred at room temp for 2 h after which time, thesolution was concentrated to dryness and treated with diethyl ether (10mL) and water (5 mL). The organic layer was further washed with water(2×10 mL), dried (Na₂SO₄), filtered, and evaporated to dryness to givecompound 5-4 as a foam (0.450 g, 91.0%). ¹H NMR (CDCl₃): δ 1.39 (s, 3H),2.15 (s, 3H), 2.21 (s, 3H), 4.27 (m, 1H), 4.49 (dd, 1H, J=4.2, 11.9 Hz),4.57 (dd, 1H, J=6.16, 11.9 Hz), 5.14 (d, 1H, J=3.1 Hz), 6.25 (s, 1H),8.54 (s, 1H), 8.75 (s, 1H).

Step 5: Compound 5-4 (0.100 g, 0.259 mmol) was dissolved in anhydroustoluene (3.0 mL) under argon and cooled to −20° C. DAST (0.2 mL, 1.55mmol) was added slowly and the cooling bath was removed after theaddition was complete. Stirring was continued for 1 h and the mixturewas poured into satd NaHCO₃ (100 mL) and washed until gas evolutionceased. The organic phase was dried (Na₂SO₄), concentrated, and purifiedby silica gel chromatography eluting with 30% Et₂O-petroleum ether gavepure 5-5 (0.028 g, 27.9%). ¹H NMR (CDCl₃): δ 1.24 (d, 3H, J=22.8 Hz),2.20 (s, 3H), 2.22 (s, 3H), 4.41-4.55 (m, 3H), 4.47 (dd, 1H, J=9.2, 22.0Hz), 6.37 (d, 1H, J=17.6 Hz), 8.45 (s, 1H), 8.82 (s, 1H).

Step 6: Compound 5-5 (0.018 g, 0.047 mmol) was dissolved in methanol (5mL) and treated with a solution of sodium methoxide (3.6 mg, 0.67 mmol)in methanol (5 mL). The solution was stirred at room temp for 1 h,neutralized with concd acetic acid and chromatographed on silica geleluting with a stepwise gradient of Et₂O/methanol (0-5%) to affordcompound 5-6 (0.010 g, 70.9%). ¹H NMR (CDCl₃): δ 1.23 (d, 3H, J=22.4Hz), 4.04 (dd, 1H, J=2.11, 12.5 Hz), 4.17 (dd, 1H, J=1.5, 9.2 Hz), 4.25(dd, 1H, J=1.9, 12.3 Hz), 4.61 (dd, 1H, J=9.2, 22.3 Hz), 6.37 (d, 1H,J=17.3 Hz), 8.70 (s, 1H), 8.78 (s, 1H).

Example 4 Synthesis of (2′R)-2′-Deoxy-2′-Fluoro-2′-C-MethyladenosineStarting from (2′R)-6-Chloro-2′-Deoxy-2′-Fluoro-2′-C-Methylpurine

Step 1: Compound 5-5 (0.100 g, 0.26 mmol) was heated in a pressure tubewith methanolic ammonia (ca. 7 N, 25 mL) at 80° C. for 12 h. The crudereaction was pre-adsorbed onto silica gel and purified by columnchromatography eluting with a stepwise gradient of Et₂O-MeOH (0-5%). Theimpure product was converted to the hydrochloride salt by dissolving thecompound in a minimal amount of ethanol and treating the solution with0.5 mL of a 0.6 M HCl solution. Concentration to near dryness gavecompound 6-1 as off-white crystals (0.020 g, 24.2%). ¹H NMR (CD₃OD): δ1.19 (d, 3H, J=22.3 Hz), 3.88 (dd, 1H, J=2.7, 12.7 Hz), 4.06 (dd, 1H,J=2.1, 12.5 Hz), 4.11 (app d, 1H, J=9.2 Hz), 4.35 (dd, 1H, J=9.4, 24.5Hz), 6.35 (d, 1H, J=16.5 Hz), 8.43 (s, 1H), 8.85 (s, 1H).

Example 5 Antiviral Activity of(2′R)-2′-Deoxy-2′-Fluoro-2′-C-Methylcytidine HCV Replicon Assay

The anti-flavivirus activity of the compounds was determined asdescribed by Stuyver, et al. (“Ribonucleoside analogue that blocksreplication of bovine viral diarrhea and hepatitis C viruses inculture”, Antimicrobial Agents and Chemotherapy 47:244-254 (2003)). Thecompound was dissolved in DMSO and added to the culture media at finalconcentrations ranging from 3 to 100 μM. A 4-days incubation resulted indose-dependant reduction of the replicon HCV RNA (FIG. 1A). A 1-logreduction of replicon RNA (or EC₉₀ value) was reached at approximately2.5 μM. Measurement of the reduction of rRNA gave an indication of theinhibitory effect on cellular polymerases. Subtraction of this cellulartoxicity value from the antiviral values resulted in the therapeuticindex line and EC₉₀ value. Based on these calculations, an average EC₉₀value, corrected for cellular toxicity, of approximately 2.5 μM wasobtained. FIG. 1A shows the dose-dependant reduction of the replicon HCVRNA based on the treatment with(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine. The viral reduction wascompared to the reduction of cellular RNA levels (ribosomal RNA) toobtain therapeutic index values. EC₉₀ represents the effectiveconcentration 90% at 96 hours following the dose dependantadministration of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine. FIG. 1Bshows the prolonged reduction in replicon HCV RNA up to 7 days followingtreatment with 5 and 25 μM.

The activity of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine in thereplicon system is summarized in Table 1. The EC₉₀ values for(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine as well as2′-C-methylcytidine and 2′-C-methyladenosine are shown for threeseparate replicon clones (HCV-WT (Wild Type), 9-13 and 21-5) as well astwo other clones (S282T and rRNA). The EC₉₀ values for(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine were in the range of 1.6 to4.6 μM for the replicon clones. In contrast the EC₉₀ values for2′-C-methylcytidine were in the range of 6.6-37.4 μM. Interestingly, theEC₉₀ values for 2′-C-methyladenosine were comparable to those of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine. The activity of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine and 2′-C-methylcytidine inother replicons tested is shown in Table 2.

Polymerase Assay

Table 3 shows the potency of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine-5′-triphosphate (TP) in theNS5B polymerase assay. The inhibitory concentration 50% was determinedto be in the range of 1.7 to 7.7 μM.

Toxicity

A summary of the toxicity data for(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine using the mitochondrialtoxicity assay is shown in Tables 6 and 7. Table 7 shows the lack ofeffects of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine and2′-C-methylcytidine on mitochondrial DNA synthesis and lack of effectson lactic acid increase in this assay. Results shows the relative lackof toxicity of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine. Table 6shows a cytotoxicity analysis in various cell lines (Clone A, Huh7,HepG2, MDBK, PBM, CEM, Vero, MRC-5). Cytotoxic concentration 50% (CC₅₀)was greater than 75-100 μM in all clones tested for(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine as well as2′-C-methylcytidine. In contrast is the relative toxicity of2′-C-methyladenosine.

The effects the nucleoside analogs tested on human bone marrow cells isdepicted in Table 9. As shown, the IC₅₀ values for2′-methyl-2′-fluorocytidine were significantly higher (98.2, BFU-E) and93.9 (CFU-GM) as compared to 2′-methylcytadine or AZT. Results show that2′-methyl-2′-fluorocytidine was significantly less toxic than comparedto the other nucleoside compounds.

Animal Studies

FIG. 2 depicts the average weight change (%) of female Swiss mice invivo the toxicity analysis of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine at various doses.Intraperitneal injections were given on days 0 to day 5 of the 0, 3.3,10, 33, 100 mg/kg. Each dosing group contained 5 mice and no mice diedduring the 30-day study. No significant toxicity was observed in themice.

FIG. 3 and Table 6 summarize the pharmacokinetic parameters of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine in Rhesus monkeys given asingle dose (33.3 mg/kg) oral (Table 6, FIG. 3) or intravenous dose(FIG. 3) of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine.

Other Antiviral Activity

Summary of the range of antiviral activity of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine is shown in Table 4. Tableshows that in addition to HCV virus(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine shows activity againstRhinovirus, West Nile virus, Yellow Fever virus, and Dengue virus.

Table 5 shows the lack of activity of(2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine on HCV surrogate modelsBVDV as well as other viruses including HIV, HBV and Corona virus. Incontrast, 2′-C-methylcytidine and 2′-C-methyladenosine show greateractivity in the HCV surrogate model, BVDV. These results show thenecessity for screening this series of compounds against the HCVreplicon system versus surrogate HCV systems.

TABLE 1 Summary of the Anti-HCV Replicon Activity of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine* (2′R)-2′-deoxy- 2′-fluoro-2′-C- 2′-C-2′-C- Replicon methylcytidine methylcytidine methyladenosine HCV-WT 1b4.6 ± 2.0 21.9 ± 4.3  2.1 ± 0.27 S282T mut. 1b 30.7 ± 11.7 37.4 ±12.1 >100 9-13 (subgenomic) 4.6 ± 2.3 13.0 0.7 21-5 (full-length) 1.6 ±0.7  6.6 0.6 *Values represent EC₉₀ (μM)

TABLE 2 Activity of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine and2′-C- methylcytidine in other Replicons (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine 2′-C-methylcytidine IC₉₀ IC₉₀ EC₉₀ (μM) EC₉₀ (μM)Replicon (μM) GAPDH MTT (μM) GAPDH MTT 1b (Ntat) 3.8 >100 >10027.2 >100 >100 1b (Btat) 11.5 >100 >100 31.1 >100 >100 1a 34.7 >100 >10035.0 >100 >100 (pp1aSI-7)

TABLE 3 HCV 1b NS5B Polymerase Assay (IC₅₀, μM) (2′R)-2′-deoxy-2′- 2′-C-fluoro-2′-C- 2′-C-methylcytidine methyladenosine methylcytidine TP TP TPWild-Type 1.7 ± 0.4^(a)  6.0 ± 0.5 20.6 ± 5.2 NS5B 7.7 ± 1.2^(b) S282T2.0^(a) 26.9 ± 5.5 >100 8.3 ± 2.4^(c) ^(a)Values determined using batch1; ^(b)Value determined using batch 2 and 3; and ^(c)Value determinedusing batch 2.

TABLE 4 Summary of Antiviral Activity of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine EC₅₀, CPE EC₅₀, NR^(a) CC₅₀, CPE CC₅₀, NR^(a) Virus Cell(μM) (μM) (μM) (μM) West Nile Vero 32 12 >100 32 Dengue Vero32/55 >100/>100 >100 >100 Type 2 Yellow Vero  19/3.2 32/12 >100 >100Fever Influenza A MDCK >100 >100 >100 >100 (H1N1) Influenza AMDCK >100 >100 >100 >100 (H3N2) Influenza B MDCK >100 >100 >100 >100Rhinovirus KB 25 20 >100 >100 Type 2 VEE Vero >100 >100 >100 >100SARSCoV Vero >100 >100 >100 >100 ^(a)NR = Neutral Red.

TABLE 5 Summary of Antiviral Activity of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine (2′R)-2′-deoxy-2′- fluoro-2′-C- 2′-C- 2′-C-methylcytidine methylcytidine methyladenosine Virus (EC₉₀, μM) (EC₉₀,μM) (EC₉₀, μM) BVDVncp >22 0.5 1.2 BVDVcp >100 2 1.5 RSV >100 >100 >100HIV^(a) >100 ND ND HBV >10 >10 ND Coronavirus 229E >100 ND ND ND = Notdetermined.

TABLE 6 Cytotoxicity Studies^(a) (2′R)-2′-deoxy-2′- fluoro-2′-C- 2′-C-methylcytidine 2′-C-methylcytidine methyladenosine Cell Line CC₅₀, μMCC₅₀, μM CC₅₀, μM CloneA >100 >100 37 Huh7 >100 >100 30 HepG2 75 >100 58MDBK >100 >100 PBM >100 CEM >100 Vero >100 MRC-5 >100 ^(a)Resultsdetermined using MTS assay.

TABLE 7 Mitochondrial Toxicity Study mtDNA Synthesis Compound (IC₅₀, μM)Lactic Acid Increase (2′R)-2′-deoxy-2′-fluoro-2′- >25 No effect ≧ 33 μMC-methylcytidine 2′-C-methylcytidine >25 No effect ≧ 33 μM

TABLE 8 Preliminary PK Parameters in Rhesus Monkeys Following a SingleOral Dose of (2′R)-2′-deoxy-2′-fluoro-2′-C-methylcytidine at 33.3 mg/kgParameter Units Mean ± SD C_(max) μM 9.6 ± 2.7 T_(max) hours 2 ± 1AUC_(0-last) μM×h 44.2 ± 22.2 T½ hours 3.9 ± 0.1 Bioavailability F % 21± 11

TABLE 9 Effect of Nucleoside Analogs on Human Bone Marrow Cells BFU-ECFU-GM Compound (β-D-analog) IC₅₀ (μM) 2′-fluoro-2′-C- 98.2 93.9methylcytidine 2′-C-methylcytidine 20.1 13.2 AZT 0.08 0.95

1-129. (canceled)
 130. A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L) or its pharmaceutically acceptable salt of the structure:

wherein the base is a purine base represented by the following formula:

X is O, S, CH₂, Se, NH, N-alkyl, CHW (R, S, or racemic), C(W)₂, wherein W is F, Cl, Br, or I; R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate; R² is H or phosphate; R¹ and R² or R⁷ can also be linked with cyclic phosphate group; R² and R^(2′) are independently H, C₁₋₄ allyl, C₁₋₄ alkenyl, C₁₋₄ alkynyl, vinyl, N₃, CN, Cl, Br, F, I, NO2, C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄ alkynyl), C(O)O(C₁₋₄ alkenyl), O(C₁₋₄ acyl), O(C₁₋₄ alkyl), O(C₁₋₄ alkenyl), S(C₁₋₄ acyl), S(C₁₋₄ alkyl), S(C₁₋₄ alkynyl), S(C₁₋₄ alkenyl), SO(C₁₋₄ acyl), SO(C₁₋₄ alkyl), SO(C₁₋₄ alkynyl), SO(C₁₋₄ alkenyl), SO₂(C₁₋₄ acyl), SO₂(C₁₋₄ allyl), SO₂(C₁₋₄ alkynyl), SO₂(C₁₋₄ alkenyl), O₃S(C₁₋₄ acyl), O₃S(C₁₋₄ alkyl), O₃S(C₁₋₄ alkenyl), NH₂, NH(C₁₋₄ alkyl), NH(C₁₋₄ alkenyl), NH(C₁₋₄ alkynyl), NH(C₁₋₄ acyl), N(C₁₋₄ alkyl)₂, N(C₁₋₁₈ acyl)₂, wherein alkyl, alkynyl, alkenyl and vinyl are optionally substituted by N₃, CN, one to three halogen (Cl, Br, F, I), NO₂, C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄ alkyl), C(O)O(C₁₋₄ alkynyl), C(O)O(C₁₋₄ alkenyl), O(C₁₋₄ acyl), O(C₁₋₄ alkyl), O(C₁₋₄ alkenyl), S(C₁₋₄ acyl), S(C₁₋₄ allyl), S(C₁₋₄ alkynyl), S(C₁₋₄ alkenyl), SO(C₁₋₄ acyl), SO(C₁₋₄ alkyl), SO(C₁₋₄ alkynyl), SO(C₁₋₄ alkenyl), SO₂(C₁₋₄ acyl), SO₂(C₁₋₄ alkyl), SO₂(C₁₋₄ alkynyl), SO₂(C₁₋₄ alkenyl), O₃S(C₁₋₄ acyl), O₃S(C₁₋₄ alkyl), O₃S(C₁₋₄ alkenyl), NH₂, NH(C₁₋₄ alkyl), NH(C₁₋₄ alkenyl), NH(C₁₋₄ alkynyl), NH(C₁₋₄ acyl), N(C₁₋₄ alkyl)₂, N(C₁₋₄ acyl)₂, OR⁷; R² and R²′ can be linked together to form a vinyl optionally substituted by one or two of N₃, CN, Cl, Br, F, I, NO₂; R⁶ is an optionally substituted alkyl (including lower alkyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro; R⁴ and R⁵ are independently H, halogen including F, Cl, Br, I, OH, OR′, SH, SR′, NH₂, NHR′, NR′₂, lower alkyl of C₁-C₆, halogenated (F, Cl, Br, I) lower allyl of C₁-C₆, lower alkenyl of C₂-C₆, halogenated (F, Cl, Br, I) lower alkenyl of C₂-C₆, lower alkynyl of C₂-C₆ such as C≡CH, halogenated (F, Cl, Br, I) lower alkynyl of C₂-C₆, lower alkoxy of C₁-C₆ such as CH₂OH and CH₂CH₂OH, halogenated (F, Cl, Br, I) lower alkoxy of C₁-C₆, lower hydroxyalkyl, CO₂H, CO₂R′, CONH₂, CONHR′, CONR′₂, CH═CHCO₂H, CH═CHCO₂R′; and R′ is an optionally substituted alkyl of C₁-C₁₂, cycloalkyl, optionally substituted alkynyl of C₂-C₆, optionally substituted lower alkenyl of C₂-C₆ or optionally substituted acyl. when n is 1, then R⁴ is ═O. when n is 0, then a double bond exists between position 1 and position
 6. 131. The (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) of claim 130 or its pharmaceutically acceptable salt thereof, wherein the Base is represented by the following formula:

when n is 0, then R⁴ is NH₂, R⁵ is H and a double bond exists between position 1 and position 6; when n is 1, then R⁴ is ═O and R⁵ is NH₂.
 132. A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L) or its pharmaceutically acceptable salt of the structure:

wherein the base is a purine base; X is O, S, CH₂, Se, NH, N-alkyl, CHW (R, S, or racemic), C(W)₂, wherein W is F, Cl, Br, or I; R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower allyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate; R² is H or phosphate; R¹ and R² or R⁷ can also be linked with cyclic phosphate group.
 133. The (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) of claim 132 or its pharmaceutically acceptable salt thereof, wherein the Base is represented by the following formula:

when n is 0, then R⁴ is NH₂, R⁵ is H and a double bond exists between position 1 and position 6; when n is 1, then R⁴ is ═O and R⁵ is NH₂.
 134. A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted alkyl (including lower allyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro.
 135. A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:


136. A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate.
 137. A (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:


138. A pharmaceutical composition comprising the nucleoside of claim 130 or its pharmaceutically acceptable salt and a pharmaceutically acceptable carrier.
 139. A pharmaceutical composition comprising the nucleoside of claim 131 or its pharmaceutically acceptable salt and a pharmaceutically acceptable carrier.
 140. A pharmaceutical composition comprising the nucleoside of claim 132 or its pharmaceutically acceptable salt and a pharmaceutically acceptable carrier.
 141. A pharmaceutical composition comprising the nucleoside of claim 133 or its pharmaceutically acceptable salt and a pharmaceutically acceptable carrier.
 142. A pharmaceutical composition comprising a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L), or its pharmaceutically acceptable salt thereof, in a pharmaceutically acceptable carrier, of the formula:

wherein R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, allyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted allyl (including lower alkyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro.
 143. A pharmaceutical composition comprising a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D or β-L), or its pharmaceutically acceptable salt thereof in a pharmaceutically acceptable carrier of the formula:


144. A pharmaceutical composition comprising a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D), or its pharmaceutically acceptable salt thereof in a pharmaceutically acceptable carrier of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate.
 145. A pharmaceutical composition comprising a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D), or its pharmaceutically acceptable salt thereof in a pharmaceutically acceptable carrier of the formula:


146. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 130 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 147. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 131 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 148. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 132 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 149. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 133 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 150. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted alkyl (including lower alkyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro. optionally in a pharmaceutically acceptable carrier.
 151. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 152. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate. optionally in a pharmaceutically acceptable carrier.
 153. A method for the treatment or prophylaxis of Hepatitis C infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 154. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 130 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 155. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 131 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 156. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 132 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 157. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 133 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 158. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted alkyl (including lower alkyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro. optionally in a pharmaceutically acceptable carrier.
 159. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 160. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate. optionally in a pharmaceutically acceptable carrier.
 161. A method for the treatment or prophylaxis of Rhinovirus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 162. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 130 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 163. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 131 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 164. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 132 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 165. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 133 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 166. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower allyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted alkyl (including lower allyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro. optionally in a pharmaceutically acceptable carrier.
 167. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 168. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted Carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate. optionally in a pharmaceutically acceptable carrier.
 169. A method for the treatment or prophylaxis of Yellow Fever Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 170. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 130 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 171. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 131 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 172. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 132 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 173. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 133 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 174. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ and R⁷ are independently H, phosphates including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted alkyl (including lower alkyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro. optionally in a pharmaceutically acceptable carrier.
 175. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 176. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate. optionally in a pharmaceutically acceptable carrier.
 177. A method for the treatment or prophylaxis of West Nile Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 178. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 130 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 179. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 131 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 180. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 132 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 181. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of the nucleoside of claim 133 or its pharmaceutically acceptable salt optionally in a pharmaceutically acceptable carrier.
 182. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ and R⁷ are independently H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including allyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ or R⁷ is independently H or phosphate; R¹ and R⁷ can also be linked with cyclic phosphate group; and R⁶ is an optionally substituted alkyl (including lower allyl), cyano (CN), CH₃, OCH₃, OCH₂CH₃, hydroxy methyl (CH₂OH), fluoromethyl (CH₂F), azido (N₃), CHCN, CH₂N₃, CH₂NH₂, CH₂NHCH₃, CH₂N(CH₃)₂, alkyne (optionally substituted), or fluoro. optionally in a pharmaceutically acceptable carrier.
 183. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 184. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

wherein R¹ is H, phosphate, including monophosphate, diphosphate, triphosphate, or a stabilized phosphate prodrug, H-phosphonate, including stabilized H-phosphonates, acyl, including optionally substituted phenyl and lower acyl, alkyl, including lower alkyl, O-substituted carboxyalkylamino or its peptide derivatives, sulfonate ester, including alkyl or arylalkyl sulfonyl, including methanesulfonyl and benzyl, wherein the phenyl group is optionally substituted, a lipid, including a phospholipid, an L or D-amino acid (or racemic mixture), a carbohydrate, a peptide, a cholesterol, or other pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R¹ is H or phosphate. optionally in a pharmaceutically acceptable carrier.
 185. A method for the treatment or prophylaxis of Dengue Virus infection comprising administering to a host an antivirally effective amount of a (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside (β-D) or its pharmaceutically acceptable salt thereof of the formula:

optionally in a pharmaceutically acceptable carrier.
 186. The method of claim 146, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 187. The method of claim 151, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 188. The method of claim 153, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 189. The method of claim 154, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 190. The method of claim 159, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 191. The method of claim 161, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 192. The method of claim 162, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 193. The method of claim 167, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 194. The method of claim 169, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 195. The method of claim 170, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 196. The method of claim 175, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 197. The method of claim 177, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 198. The method of claim 178, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 199. The method of claim 183, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.
 200. The method of claim 185, wherein the antivirally effective amount of (2′R)-2′-deoxy-2′-fluoro-2′-C-methyl nucleoside is administered in combination or alternation with at least one treatment selected from the group consisting of: interferon, including interferon alpah 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin 10 and interleukin 12; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor, and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a 1-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazole; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate. 